President Mwai Kibaki will travel to Addis Ababa for the 53-nation African Union meeting, a forum where his country is more used to playing the role of regional peacemaker than a cause of continental concern.

Political and ethnic violence has killed 850 people in Kenya since Kibaki's disputed re-election on December 27, a wave of instability that has shocked its neighbours and Western donors and battered its image as a stable trade and tourism hub.

"Kenyans are killing one another at an alarming rate and are putting the country in grave danger of civil war," said Jennifer Windsor, executive director of U.S.-based rights group Freedom House.

Many Kenyans fear what will happen if Annan's mediation fails to force an agreement between Kibaki and his rival Raila Odinga, leader of the opposition Orange Democratic Movement (ODM) who says the presidential poll was rigged.

The leaders of Britain, France, Germany, Italy and the European Union threw their weight behind the former U.N. Secretary-General's efforts at a meeting in London on Tuesday.

ETHNIC CLEANSING

Jendayi Frazer, the top U.S. diplomat for Africa, said on Wednesday the violence had degenerated into ethnic cleansing in parts of the Rift Valley and said she wanted to see "some kind of power-sharing and some kind of coalition government".

Annan launched formal mediation between Kibaki's Party of National Unity (PNU) and the ODM on Tuesday, each side represented by a team of three. There were no talks on Wednesday but U.N. officials said meetings would resume on Thursday.

Kenya's unrest may have been triggered by an election dispute but the violence has taken on an ethnic dimension of its own, with members of Kibaki's Kikuyu tribe and the Luos, Luhyas and Kalenjins who largely back Odinga apparently locked in a spiral of tit-for-tat attacks.

After a month of bloodshed, the Kenyan authorities have vowed to adopt a tougher approach to prevent the conflicts escalating out of control.

Kibaki said on Wednesday the security forces were under strict orders to take firm action against anyone inciting violence. Odinga accused him of ordering an "inhumane and barbaric" shoot-to-kill policy.

Military helicopters fired rubber bullets on Tuesday over an angry mob in the Rift Valley town of Naivasha, scene of some of the bloodiest unrest in recent days, and the more muscular tactics appear to have had some effect.

Some people have started returning to work in the town, although thousands forced from their homes are still sheltering under armed guard in its police station and prison.

But near Nderi, just 20 minutes from Nairobi, youths burned branches and piled rocks to block the road from the Rift Valley on Wednesday, raising fears that the ethnic mob violence seen there in recent days could be getting closer to the capital.