"If Kenya burns, what is left?" the African Union's top diplomat, Alpha Oumar Konare, said in an opening speech to a three-day summit, echoing widespread shock at the once stable country's plunge into turmoil.

U.N. Secretary-General Ban Ki-moon told the leaders, meeting in neighbouring Ethiopia, that the violence which has killed 850 people was "threatening to escalate to catastrophic levels".

Ban, who met President Mwai Kibaki at the summit, said he would fly to Kenya on Friday to help mediation efforts by his U.N. predecessor Kofi Annan.

In a sign of a mounting international drive to end Kenya's crisis, South African President Thabo Mbeki told Reuters influential business tycoon Cyril Ramaphosa would also head to Nairobi on Friday to join Annan's team.

South Africa says Kenya's turmoil could be disastrous for the continent if it does not end soon. Ramaphosa was chief negotiator for the African National Congress in talks that produced a peaceful end to apartheid in 1994.

Konare told the 53-nation organisation Africa could not "sit with our hands folded" and Senegal's President Abdoulaye Wade struck a similar theme, saying before the summit that Kenya must top discussions.

"It is Africa's image which is at stake in this Kenya affair," Wade told Radio France International.

Kenya's crisis, triggered by the disputed re-election of Kibaki on December 27, is expected to sideline the summit's official theme of industrial development.

WAY OUT

Diplomats said the talks led by Annan were seen as the only way out and the international community was trying to press Kibaki and opposition leader Raila Odinga to negotiate.

The outgoing AU chairman, Ghanaian President John Kufuor, told Reuters: "The most important thing is that they keep talking."

Ban said in his speech the two men must do everything possible to end the crisis. Kibaki will fly back to Nairobi on Friday and Ban plans to meet Odinga in the Kenyan capital.

The opposition leader says he is the rightful president and that the poll was rigged. Kibaki says he has been duly elected.

The AU followed its traditional policy by inviting only Kibaki to Addis Ababa as the head of a sitting government but Odinga said on Thursday he should be representing Kenya and Wade also said Odinga should be invited.

Odinga told Reuters the AU must not echo the policies of its discredited predecessor, the Organisation of African Unity, in "tolerating dictators in the name of non-interference".

A second round of negotiations led by Annan was postponed for 24 hours on Thursday after a policeman killed an opposition legislator in the Rift Valley.

About 850 people have been killed and some 250,000 people have fled their homes since a cycle of ethnic bloodshed began a month ago, turning Kenya into Africa's biggest current headache.

But it is not the only problem facing the AU. Anarchic Somalia and the crisis in Sudan's Darfur region will also be discussed at the summit.

Ban urged the leaders of Sudan and Chad to exercise maximum restraint after N'Djamena said on Thursday rebels backed by Khartoum were advancing on the Chadian capital.