In Chad, government forces were clashing with rebels for a third day with gunfire and shelling heard throughout the city. Thousands of people were fleeing, and casualties were believed to be high. -- PHOTO: AP

The downtown embassy, which was hit by indirect fire during weekend clashes, is now vacant and unprotected. The US State Department warned rebels on Monday not to enter the compound, which remains sovereign US territory.

'We would tell anybody who has any thoughts of entering the embassy grounds that that is American territory, leave it immediately and do not attempt to enter any of the buildings,' spokesman Sean McCormack said.

He said the warning is being sent to the rebels 'through various channels' but acknowledged there was no guarantee the compound would not be breached.

At the same time, he said that suspected Sudanese support for the rebels was 'very worrying', and Washington has told Sudan's government to end such support and press the rebels to withdraw.

Those messages were conveyed directly to the Sudanese presidency and Foreign Ministry by the top US diplomat in Khartoum, he said.

The rebels arrived on the capital's outskirts on Friday after a three-day push across the desert from Chad's eastern border with Sudan. The situation in N'Djamena deteriorated over the weekend to the point where the State Department ordered several dozen nonessential US Embassy staff and their families to leave the country.

The four who remain - Ambassador Louis Nigro, a defence attache, political counselor and security officer - shredded and burned sensitive documents and removed the flag from the compound on Saturday before heading to the airport where they are now based, officials said.

Mr McCormack said the decision to abandon the embassy, a rare step believed to be the first such move since the US mission to Liberia was fully evacuated during that country's civil war, was made because of a 'very fluid' security situation but stressed he expected the diplomats to return once conditions improve.

The State Department has urged US citizens to leave Chad, and officials said some fewer than 100 of the roughly 500 registered with the embassy were known to have left.

Without any personnel at its embassy, the State Department has set up two telephone numbers to report the presence and whereabouts of Americans in Chad.

However, on Sunday, the department said its ability to help Americans in Chad was 'extremely limited' and asked those who wished to be evacuated to 'prepare to depart immediately and identify themselves to the French military, who will retrieve American citizens to escort them to the airport'.

France, the former colonial power, has a long-standing military presence in Chad and is evacuating hundreds of foreigners from the country.

On Monday, the United Nations Security Council strongly condemned the rebel attacks, and it gave approved intercession by France and other countries to help the government repel the threat.

In Chad, government forces were clashing with rebels for a third day with gunfire and shelling heard throughout the city. Thousands of people were fleeing, and casualties were believed to be high.

Mr Stephen J. Hadley, President George W. Bush's national security adviser, said on Monday that the way forward in dealing with the conflict 'is to get both of these governments to recognise that they have an obligation to their peoples to agree to end the support of these reciprocal rebel groups and allow the international community in to ensure people can be resettled and humanitarian systems can get in place'.

'The people of both countries are paying the price,' Mr Hadley said in remarks to the Carnegie Endowment for International Peace. -- AP