People fleeing the Chadian capital N'Djamena. The UN High Commissioner for Refugees (UNHCR) said that between 15,000 and 20,000 Chadians have taken refuge in Cameroon to escape fighting between rebels and government forces. -- PHOTO: AFP

'I am alarmed by the deteriorating security situation in the capital, N'Djamena, and elsewhere,' he said. 'We can no longer guarantee the safety and security of UN staff in Chad and we have evacuated, with the help of the French Government, most of the personnel into neighbouring countries, in Cameroon and Gabon.'

Mr Ban said he was leaving in place a small number of UN peacekeepers and other personnel in Chad's capital, and that the UN would do as much as it could to help resolve the crisis.

'I welcome the initiative of the African Union to have designated leaders of Libya and the Republic of Congo to mediate this issue,' he said.

Mr Ban also called on the UN Security Council 'to help bring this terrible crisis to an end. It has devastating consequences not only for the people of Chad and Darfurian refugees seeking shelter there, but also for Darfur itself.'

The fierce fighting between rebels and government forces in N'Djamena have left hundreds of civilians dead, with insurgents agreeing to a cease-fire and France, the colonial power, threatening to back up the government.

A group of high-level officials was to have left Republic of Congo for Chad on Tuesday afternoon on a mediation mission, but did not depart because they were still awaiting authorisation from the Chadian government. Libya, which has mediated in the past among Chadian groups and between Chad and Sudan, also was trying to broker peace. -- AP