Chad UFDD forces have attacked the capital in a bid for political power.
Originally uploaded by Pan-African News Wire File Photos
The rebels reached the presidential palace at the weekend
The United Nations Security Council has called on all member-states to back the Chadian government following two days of clashes with rebels in Ndjamena.
Correspondents say this will be taken by former colonial power France, which has a base in Chad, as an endorsement of the support it has been providing.
But France's Foreign Minister, Bernard Kouchner, later said he did not foresee it launching any military operations.
Earlier, thousands of people fled the capital during a lull in fighting.
Many crossed the river border with Cameroon via the Ngueli bridge or by using boats.
Local officials told the UN refugee agency, the UNHCR, that thousands were also crossing at the border town of Kousseri and that more were expected.
A plane chartered by the French government carrying 363 foreigners evacuated from Chad arrived in Paris on Monday morning.
The Chadian government earlier said it had driven the rebels out of the city, but the rebels insisted they had only made a tactical withdrawal and would be launching a fresh assault.
Aid workers have reported hundreds of injuries to civilians resulting from the intense battles near the presidential palace, with bodies lying in the streets.
After a late night negotiating session, UN diplomats agreed a statement on Monday morning condemning the attacks by the rebels, who want to overthrow President Idriss Deby, and demanding an end to the violence.
The non-binding statement also gave the green light for countries to "provide support, in conformity with the United Nations Charter, as requested by the government of Chad".
French diplomatic tight-rope
Chad's permanent representative to the UN, Mahamat Adoum, wrote to the Security Council on Sunday, appealing for countries to "to provide all aid and assistance needed to help it".
The BBC's Laura Trevelyan in New York says the move will be taken by France, which has 1,400 troops based in Chad, as an endorsement of the support it has been giving the government.
The US permanent representative, Zalmay Khalilzad, said "the French have the expertise and lead on this issue, and should they decide to do more, they have the support of the Security Council".
However, the French foreign minister later said he "hoped" his country's armed forces would "not have to intervene further" to support President Deby.
"We do not intend to put French troops more on alert than they are, or to start military operations," he said.
"When it was necessary to defend the airport - something which went on for a very short time, moreover - our forces did so very briskly, very effectively," he added, referring to a rebel attack on Saturday.
The rebels have previously threatened to attack a French-dominated European Union peacekeeping force, because of France's support to the government.
The deployment of that force has been delayed because of the latest fighting.
Mr Kouchner said that most of N'Djamena was in the government's hands, but cautioned that the rebels were still operating on its outskirts.
"For the time being, the city is under the control of the legal authorities," he said.
'Window on genocide'
Earlier, the commander the Chadian government forces, Gen Mahamat Ali Abdallah, said the rebels had been "completely routed" in the capital.
However, a rebel spokesman, Abderaman Koulamallah, later rejected the claim.
"We have pulled out of the city and we are waiting for the civilian population to be evacuated," he told AFP news agency.
"We certainly will go back on the offensive... We're asking the civilian population of N'Djamena to leave immediately because their safety cannot be assured."
The army has also said it had thwarted a second rebel attack on Adre, near the border with Sudan over the weekend.
The town is where some 240,000 refugees from Darfur are based, living in camps and where the EU force is due to deploy.
The 3,700-strong EU force is intended to protect refugees from the Darfur region of neighbouring Sudan, as well as aid workers.
Chad has accused the Sudanese government of backing the rebel offensive in Chad in order to stop the EU force from being sent to the region.
Sudan denies this, as well as accusations that it has supported Arab militias accused of ethnic cleansing and genocide in Darfur.
"Sudan does not want this force because it would open a window on the genocide in Darfur," said Chadian Foreign Minister Amad Allam-Mi.
The UN Security Council statement issued on Monday did not directly mention Khartoum, but instead called on all countries in the region to put an end to the activities of armed groups and to respect common borders.
The recent violence began on Saturday, when the rebels seized control of large parts of the capital, approaching the palace where President Deby was holding out.
Mr Deby seized power in a coup in 1990, but has won three elections since then, although their legitimacy has been challenged.
MONDAY, FEBRUARY 04, 2008
2:01 MECCA TIME, 23:01 GMT
UN condemns Chad rebel attack
The French military has been helping foreign citizens flee the fighting in Ndjamena
The UN Security Council has strongly condemned the rebel attack on Chadian capital Ndjamena and given other countries the green light to help the government repel the rebels.
Monday's non-binding statement came as rebels, who had pulled back a day earlier, allowing tens of thousands of residents to flee, renewed their assault on the city.
"The Security Council calls upon member states to provide support in conformity with the United Nations charter as requested by the government of Chad," Ricardo Alberto Arias, Panama's ambassador and the current council president, said.
The rebels are seeking to topple Idriss Deby, Chad's president.
An initial French draft had called on UN members to support Deby "by all necessary means", but the final wording was changed to satisfy Russian objections to what was seen as a reference to military aid.
Chad violence escalates
Speaking before the Security Council issued its statement, Nicolas Sarkozy, the French president, said France and the EU would send troops only with the council's approval.
"We must avoid a conflict in Chad by supporting the legitimate government," Sarkozy said during a visit to Bucharest.
"In no region should weapons be a way to come to power."
But Bernard Kouchner, the French foreign minister, said Ndjamena was under government control for now and he did not foresee French troops entering combat.
"We do not have the intention of putting French troops on alert more than they already are and of launching military operations," he said in Paris.
There were reports of renewed shelling on Monday in Chad, as rebels returned to the city.
Inside Ndjamena the scene was "bloody and chaotic", one aid worker was quoted by the Associated Press as saying.
Aid agencies also said that hundreds of civilians had been injured by stray bullets.
There has been no indication of the toll from the two days of fighting but Medecins sans Frontieres, the international medical organisation, said it had operated on about 50 people in the capital.
The French military, which has been flying foreigners from Ndjamena to Gabon, said on Monday under 300 foreign nationals were still waiting to be evacuated from the capital.
The rebels first attacked Ndjamena on Friday.
A force of 1,000-1,500 fighters, equipped with pickup trucks mounted with machine guns, arrived on the capital's outskirts after a three-day push across the desert from Chad's eastern border with Sudan.
A ceasefire signed between Deby and four rebel groups in October recently collapsed.
The largest rebel group, the Union of Forces for Democracy and Development, is led by a former minister who accuses Deby of corruption.
They penetrated the city early on Saturday, reportedly trapping Deby in his palace.
The government launched a counterattack on Sunday and the rebels pulled back that evening in what they said was a tactical withdrawal to give Ndjamena's inhabitants a chance to flee.
Analysts fear the fighting could broaden into a wider regional conflict.
Monday's UN statement also urged "all states in the region ... [to respect] their common border".
Some Chadian officials have charged that Sudan supported rebel attacks on a town close to Sudan's Darfur region, though Khartoum has denied any involvement.
The US said on Monday that it had warned the Sudanese government to stop any support it might be giving the rebels.
"We've gone directly to very high levels of the Sudanese government to say that if there is any support ... to these rebels, that should end immediately," Sean McCormack, the US state department spokesman, said.
For years Chad and Sudan have accused each other of supporting rebel groups in each others territory.
Source: Al Jazeera and agencies
Q&A: Chad rebellion
Fighting has broken out in the capital of Chad, N'Djamena, after rebels launched a major assault and seized control of large parts of the city.
The crisis could have major implications for attempts to end the conflict in neighbouring Darfur, since Sudan's government is accused of backing the rebels in Chad.
The BBC's Stephanie Hancock, who has covered Chad for the past two years, explains.
Q: Who are the rebels?
The rebels who attacked N'Djamena this week are a new alliance of three main groups, who joined forces just two months ago.
The largest group is UFDD (United Force for Democracy and Development), which is led by Mahamat Nouri.
He is a former member of President Idriss Deby's government and was working as Chad's ambassador to Saudi Arabia when he defected to the rebellion two years ago.
He is a Gorane, the same clan as Chad's former President Hissene Habre, whom Mr Deby ousted in a coup 17 years ago.
The second main group is RFC (Rally of Forces for Change), led by Timane Erdimi, President Deby's former chief of staff.
His role as a rebel leader is controversial as not only is he a Zaghawa, the same clan as Mr Deby, but he is also the president's own uncle.
The third rebel group if UFDD-Fondamentale, a splinter group of UFDD, currently headed by Abdelwahid Aboud.
Why are they fighting?
The rebels, as well as President Deby's political opponents, say that his rule has been both violent and corrupt.
They accuse him of favouring members of his Zagawa clan, who make up less than 3% of Chad's population, above other citizens.
Mr Deby has packed much of his government and the army with members of his clan, or other trusted allies.
Critics say he has rigged elections to enable him stay in power, and after Chad started pumping oil in 2003, he has allegedly embezzled much of the country's oil riches.
The tide began to turn against President Deby when, against the wishes of most Chadians, he changed the country's constitution to run for an unprecedented third term in office.
This prompted a wave of desertions from the Chadian Army and sowed the seeds of today's rebellion.
Didn't the rebels nearly succeed before?
President Deby was almost toppled in April 2006, when rebels again attacked the capital.
But the attack was poorly co-ordinated, and led by only one rebel group, and once they got to N'Djamena, the fighters were simply outnumbered and overpowered.
This time things have been much better planned.
Three rebel groups have been able to work as one unit, and more than 2,000 men took part.
They also wrong-footed the Chadian Army, which was expecting an attack in the east of the country, where the rebels have their bases.
Using the element of surprise, the rebels were able to cross more than 1,000km (620 miles) of terrain virtually unchallenged, and eventually enter the capital with surprising ease.
Is Sudan backing the rebels?
Khartoum has repeatedly denied backing the rebels, but it is well known that the Sudanese government does support them.
It provides not only weapons and vehicles, but also uniforms and medical supplies.
Sudan is backing the Chadian rebels to counter the threat that it faces from its own rebels in Darfur.
Many Darfur rebels are from the same ethnic group as President Deby, and ever since their uprising began, he has offered them support.
The Darfur rebels enjoy a free reign in Chad, and are so close to President Deby that it is not uncommon for them to fight alongside the Chadian Army when it needs help.
Sudan has reacted to this by, in turn, arming Chadian rebels.
What are the possible implications for Darfur?
In the short term, aid organisations will be anxious about the fate of 250,000 Sudanese refugees in eastern Chad, as well of tens of thousands of Chadian displaced people who have been affected by the spill over of violence.
If insecurity continues, getting in supplies will become increasingly difficult, and with soldiers and rebels now concentrated miles away in the capital, a security vacuum could put aid workers and the displaced at risk.
In the long term, because the Darfur crisis is intimately linked to Chad-Sudan relations, the outlook is uncertain.
As long as Chad and Sudan continue to wage war on each other, the Darfur crisis will be almost impossible to resolve.
What is likely to happen to the EU mission to eastern Chad, to protect refugees from Darfur?
Chad says the timing of the current assault is an attempt to stop EU soldiers being deployed.
But despite the violence of the past few days, the EU insists its planned peacekeeping mission will go ahead, and says the deployment has simply been delayed by a few days.
The reality is more complicated.
Should President Deby be toppled, it is not known whether Chad's new leader would still accept foreign troops, and any new regime could put a stop to deployment.
If Mr Deby stays in power, but security remains dire, it may be too risky to deploy foreign troops as they could potentially get caught up in a war they could neither understand nor control.
France, which spearheaded the mission and is providing most of the troops, risks huge loss of face if the deployment is cancelled.