Kenyan police used tear gas and water cannon Thursday to disperse protestors marching on Nairobi city centre to attend a banned rally organised by defeated presidential challenger Raila Odinga.

Odinga had called for one million supporters to gather in a Nairobi park to protest the result of last week's election in which President Mwai Kibaki was re-elected amid widespread allegations of vote-rigging.

The disputed poll triggered a wave of violence that has killed more than 340 people and displaced tens of thousands, mainly in western regions.

Police fired tear gas and warning shots after youths set fire to barricades on one of the capital's main thoroughfares and headed for Uhuru (independence) Park, where decades of Kenya's history have been shaped.

A senior police official said there were around 2,000 demonstrators and accused them of criminal intent.

"We have dispersed them because they were planning to loot Nakumatt market and we will not allow them into the city centre," police commander Herbert Khaemba told AFP.

Undeterred by a phalanx of Israeli-trained and well-equipped paramilitary police, orange-clad protestors poured out of Kibera -- Africa's largest slum -- looking for cracks in the tight security set-up.

"If they block the meeting today, there will be no peace. This is revolution", said Paul Onyango Sati, a 29-year-old unemployed Kibera resident.

Many feared a fresh eruption of violence even as diplomatic efforts to resolve the crisis intensified.

The chairman of the African Union John Kufuor was expected to arrive to press a mediation effort, along with the head of the Commonwealth observer mission in Kenya, Sierra Leonean former president Ahmed Tejan Kabbah.

South African Nobel peace laureate Desmond Tutu arrived on Wednesday in an apparent bid to persuade Kibaki and Odinga to sit down together.

The two men belong to different tribes and have traded accusations of inciting acts of genocide and ethnic cleansing.

Odinga intends to use Thursday's rally to present himself as the "people's president".

The rally "is just a beginning, but I think it is going to be a long-drawn process," Odinga said in an interview broadcast on BBC radio.

"The people want to see our democracy strengthened and expanded rather than democratic space get squeezed by this government."

The declaration on Sunday of President Mwai Kibaki's re-election and his immediate swearing in to office despite international and opposition concerns over the vote count sparked nationwide riots and tribal violence.

On Wednesday evening 36 people were reported killed in clashes, although missionaries and hospital officials said there were probably more deaths in rural areas.

The death toll since election day stood at 342, according to a tally compiled by AFP from medical workers, police officials and mortuary attendants across the country.

As pro-Odinga youths started gathering in Nairobi slums to march towards the rally's venue, police reiterated their warnings.

"Every person is once again reminded that the proposed rally has been declared illegal and any person taking part in the meeting will be dealt with according to the law," police spokesman Eric Kiraithe said.

In the western city of Kisumu, the country's third largest, police said pro-Odinga supporters also planned to demonstrate.

Meanwhile, Kenya's Red Cross appealed for emergency funds of 7.5 million dollars to help 100,000 people displaced by the violence.

Kibaki, 76, has publicly called for consultations with party leaders, but Odinga, 62, has said he will only talk once the president had acknowledged electoral fraud.

Former president Daniel arap Moi said Wednesday the unrest had sown irreversible animosity among the 40-plus ethnic groups in Kenya, which was until now considered a beacon of democracy and stability in the restive region.

Kenyan Nobel peace laureate Wangari Maathai, in an emotional televised message, also pleaded for talks and peace, while Kenya's two leading dailies had the same headline Thursday: "Save Our Beloved Country".

The government has welcomed dialogue, but said mediation was premature.

"Kenya is not at war and does not need mediators or peacekeepers," government spokesman Alfred Mutua said.

PHOTO CAPTION

A sympathizer of presidential candidate Raila Odinga runs through a cloud of tear gas.