(Adds details of AU chairman visit)

LONDON, Jan 1 (Reuters) - European states and Japan urged Kenya's political rivals on Tuesday to act responsibly to end ethnic riots that have killed almost 250 people, including villagers burned to death as they sought refuge in a church.

Britain said the heads of the African Union and Commonwealth had agreed to try to reconcile the rivals after Kenyan President Mwai Kibaki's disputed re-election in a Dec. 27 poll and accusations of vote-rigging triggered the bloodshed.

World powers warned their citizens against visiting a nation that had been seen as one of the most stable democracies on a volatile continent.

Prime Minister Gordon Brown of Britain, Kenya's former colonial power, said he had spoken to Kibaki and opposition leader Raila Odinga and urged them to seek a peaceful solution.

"I have urged both Mwai Kibaki and Raila Odinga to exercise restraint and responsible leadership," he said in a statement.

He asked Ghanaian President John Kufuor, chair of the African Union, and former Sierra Leonean President Ahmad Tejan Kabbah, head of the Commonwealth observer mission, to step in.

An AU spokesman in Ethiopia said Kufuor would visit Kibaki in Nairobi on Wednesday to discuss the crisis.

"I want to see the possibility explored where they can come together in government. But the first priority is that the violence is brought to an end. It is unacceptable that lives are being lost," Brown said.

Kibaki was sworn in on Sunday after official election results showed he had narrowly beaten Odinga.

Both sides have accused the other of vote-rigging in the presidential and parliamentary ballots. The EU observer mission said in its assessment the votes had "fallen short of key international and regional standards for democratic elections".

PEACEFUL SOLUTION

Japanese Foreign Minister Masahiko Komura cancelled a visit to Kenya scheduled for this week due to the unrest, Kyodo news agency reported. The ministry said Japan regretted "confusion" in the ballot-counting and the ensuing violence, Kyodo said.

"Japan calls upon leaders of the government and opposition parties to begin talks aimed at reconciliation so as to avoid a regression in Kenya's democracy," a ministry press officer said.

France and Germany also urged Kenya's political leaders to act responsibly.

"France is concerned by the violence over the last few days in Kenya. It calls on all the political leaders to contribute to restoring calm and avoiding any kind of action that could add to the tensions," the Foreign Ministry said in statement.

German Foreign Minister Frank-Walter Steinmeier backed a demand by the EU observers for an investigation into the results and urged the political rivals to find a peaceful solution.

"Further violence must be prevented," he said.

The disputed result has ignited long-simmering tribal rivalries in one of Africa's most stable democracies and strongest economies.

About 30 villagers, including children, were killed on Tuesday when a mob set light to a church near the town of Eldoret where hundreds of Kibaki's Kikuyu tribe had taken refuge. (Reporting by Kate Kelland in London, Anna Willard in Paris and Erik Kirschbaum in Berlin; Editing by Janet Lawrence and Michael Winfrey)

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