African leaders voiced a chorus of alarm about Kenya's rapid decline from regional peacemaker to the continent's biggest concern, and called for urgent action to stop the killing.

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

UN Secretary-General Ban Ki-moon told the leaders meeting in neighbouring Ethiopia that 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 by his UN predecessor Kofi Annan.

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," he added in comments to Radio France International. Kenya's crisis, which erupted after the disputed re-election of Kibaki on December 27, is expected to sideline the summit's official theme of industrial development.

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.

Outgoing AU chairman John Kufuor, the Ghanaian president, 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 there. The opposition leader says he is rightful president and the election was rigged. Kibaki insists 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".

The 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.

Around 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 crisis.

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. Ban met Sudanese President Omar Hassan al-Bashir to discuss delays in deploying a 26,000-strong joint AU-U.N. peacekeeping force in Darfur, where international experts say some 200,000 people have been killed in years of fighting. - Reuters