By Sue Pleming

WASHINGTON, Jan 8 (Reuters) - The United States on Tuesday pressed Kenya's opposition and government to hold talks to end a political crisis as the top U.S. diplomat for Africa extended a visit to the East African nation to help reconcile the two.

"We think that it is of primary importance that they open up those channels of communication," State Department spokesman Sean McCormack said.

"They need to agree upon something that they can both live with that ends the political crisis and therefore ends the possibility of any further political violence," he added.

But Kenyan opposition leader Raila Odinga on Tuesday rejected a government offer of bilateral talks to end a crisis that has killed at least 500 people and displaced about 255,000, saying that without international mediation such a meeting would be a "sideshow."

Shunning international pressure, Kenyan President Mwai Kibaki and Odinga have still not met since violence erupted after Kibaki's disputed re-election last month.

Kibaki, who sees the crisis as a domestic issue, has been reluctant to accept international mediation despite the constant prodding of the United States and others.

The State Department's top diplomat for Africa, Jendayi Frazer, had planned to leave Nairobi on Tuesday after several days of trying to mediate but McCormack said Secretary of State Condoleezza Rice had asked her to extend her trip.

He said Frazer would make a one-day, pre-scheduled trip to the Comoros on Wednesday but immediately go back to Kenya.

In a further diplomatic push to end the crisis, African Union chairman, Ghanaian President John Kufuor, was in Kenya on Tuesday to meet Odinga and Kibaki, and McCormack said Frazer also planned to consult the AU leader on how best to proceed.

Frazer has been harshly critical of Kenya's political leaders following the election and the violence that ensued, saying earlier this week that Kenyans had been "cheated by their leadership and their institutions."

Odinga says his rival Kibaki stole the Dec. 27 election and must step down and make way for a new vote after a transitional period.

U.S. pressure to end the crisis is also coming from politicians such as Sen. Barack Obama, a Democratic hopeful for the White House, who called Odinga on Monday and also plans to speak to Kibaki.

"He urged an end to violence and that Mr. Odinga sit down without preconditions with President Kibaki to resolve this issue peacefully. Obama is attempting to reach president Kibaki," said Obama's spokesman Ben LaBott.

Obama, whose father was Kenyan and came from the same Luo tribe as Odinga, is a member of the U.S. Senate Foreign Relations Committee. Kibaki comes from the Kikuyu tribe, which has traditionally wielded strong economic power in Kenya. (Additional reporting by Mark Egan, Editing by Eric Walsh)

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