(Adds South Africa's Tutu in Nairobi, analyst quotes)

By Kwasi Kpodo

ACCRA, Jan 2 (Reuters) - Ghanaian president and African Union chairman John Kufuor prepared a mediation mission to Kenya on Wednesday to help end ethnic killing, and Nobel peace laureate Archbishop Desmond Tutu flew in to offer his help.

Amid a growing clamour for calm, the United States and former colonial ruler Britain called for restraint and dialogue as the death toll from days of violence topped 300, fuelling fears of more instability in Kenya and East Africa as a whole.

Kenyan opposition leader Raila Odinga accuses President Mwai Kibaki of rigging his re-election. The disputed outcome has sparked ethnic killings in a country often seen as a bulwark of stability in a volatile part of Africa.

Presidency aides in Ghana said Kufuor spent much of the day in meetings on the subject, considering whether to send a delegation to the east African country to mediate or go himself.

But British Prime Minister Gordon Brown, who appealed on Tuesday to Kufuor and former Sierra Leonean President Ahmad Tejan Kabbah, the head of the Commonwealth's electoral observer mission, to intervene in Kenya, said Kufuor would go in person.

"I have just talked to President Kufuor of Ghana ... I welcome his decision, that he will announce later today, that he will go to Kenya. He will meet President Kibaki and Mr Odinga tomorrow," Brown said in a statement.

"He will call on them to urge their supporters to end violence and he will work with the parties to ensure that reconciliation is brought about and perhaps a chance that some of the people who are at the moment opponents may join a government of national unity."

TUTU IN TOWN

Earlier Kufuor's office issued a statement asking the rivals to restrain their supporters to avert further violent clashes that could only lead to Kenya's destabilisation.

"Kufuor is one of the most credible and consistent champions of the more progressive aspects of African Union politics ... for that reason he should be able to bring some pressure to bear on Kibaki and Odinga," said Chris Melville, senior Africa analyst at Control Risks consultancy in London.

Tutu, a former archbishop of Cape Town and respected peace campaigner on the continent, arrived in Nairobi on Wednesday to offer his assistance in mediation, Kenyan media reported.

"Even Desmond Tutu called me from South Africa and said he wants to meet me," Kenya election commission head Samuel Kivuitu told reporters.

Kivuitu, who declared Kibaki winner of the election on Sunday, told reporters he did "not know" if Kibaki indeed won.

Brown's Foreign Secretary David Miliband and U.S. Secretary of State Condoleezza Rice issued a joint statement on Wednesday calling for restraint and intense political dialogue.

France, Germany and Japan have all also called for calm, but analysts said Western powers had limited leverage.

"Pressure from outside powers -- for example in reducing aid -- is unlikely to bring about an immediate halt to violence. It seems there is little the international community can do at this stage," said Razia Khan, Africa economist for Standard Chartered Bank. (Additional reporting by Jeremy Lovell, Peter Apps and Alistair Thomson; writing by Alistair Thomson; Editing by Alison Williams)

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