Kenya's president and his chief rival made key concessions Monday to end their election dispute, calling off protests and agreeing to talks under pressure from the United States as the death toll from a week of violence neared 500. The top American envoy to Africa said the vote count at the heart of the dispute was tampered with and both sides could have been involved. The Dec. 27 election returned President Mwai Kibaki to power for another five-year term, with his rabble-rousing opponent, Raila Odinga, coming in a close second. But even Kenyan electoral commission chairman Samuel Kivuiti, who declared Kibaki the winner, subsequently said he is not sure Kibaki won. "Yes, there was rigging," the U.S. envoy, Jendayi Frazer, told The Associated Press in an interview in Nairobi, where she has been meeting with Kibaki and Odinga for the past three days. "I mean there were problems with the vote counting process," she added. "Both the parties could have rigged." She said she did not want to blame either Kibaki or Odinga. Kenya is crucial to the United States' war on terrorism. It has turned over dozens of people to the U.S. and Ethiopia as suspected terrorists, allows American forces to operate from Kenyan bases and conducts joint exercises with U.S. troops in the region. The U.S. also is a major donor to Kenya, long seen as a stable democracy in a region that includes war-ravaged Somalia and Sudan. Aid amounts to roughly $1 billion a year, said embassy spokesman T.J. Dowling. Frazer said the violence "hasn't shaken our confidence in Kenya as a regional hub." U.S. intervention appears to be having an effect on the crisis, with both sides softening their tones since Frazer's arrival over the weekend. On Monday, Kibaki invited Odinga to a meeting at his official residence Friday to discuss how to end the turmoil, the president's news service said. Just hours earlier, Odinga called off nationwide rallies amid fears they would spark new bloodshed. Odinga's spokesman, Salim Lone, said Odinga will meet with Kibaki as long as it is part of a mediation process with African Union chairman John Kufuor, the president of Ghana. Kufuor's trip to Kenya has been delayed repeatedly as the government rejected outside mediation. But he is now expected to begin talks in Nairobi as early as Wednesday. Frazer had won an offer from Kibaki to form a unity government over the weekend. Odinga then said he was willing to drop demands that Kibaki resign and was willing to discuss sharing power, but only through a mediator empowered to negotiate an agreement that the international community would guarantee. It would be nearly impossible for Kibaki to govern without opposition support. In parliamentary elections held the same day as the presidential vote, Odinga's party won 95 of 210 seats, and half of Kibaki's Cabinet lost their seats. It was a sign of people's anger over pervasive corruption and nepotism that favored Kibaki's Kikuyu tribe, long dominant in politics and the economy. The post-election chaos has been one of the darkest times since Kenya's independence from Britain in 1963. Much of the fighting has degenerated into riots pitting other tribes against Kibaki's Kikuyu. An official in neighboring Uganda said over the weekend, 30 fleeing Kenyans were thrown into the border river by Kenyan attackers, and were presumed drowned. Two Ugandan truck drivers carrying the group said they were stopped Saturday at a roadblock mounted by vigilantes who identified the refugees as Kikuyus and threw them into the deep, swift-flowing Kipkaren River, said Himbaza Hashaka, a Ugandan border official. The drivers said none survived, Hashaka said. On Monday, the government put the death toll in election violence at 486 with some 255,000 people displaced from their homes. The toll, which did not include the drownings at the border, was compiled by a special committee of humanitarian services set up by the government which extensively toured areas most affected by riots. The body of Olympian Lucas Sang was found in western Kenya New Year's Eve with a deep gash to the back of his head and severe burns, said close friend Moses Tanui, a former world 10,000-meter champion. Sang, who was in his 50s, was a 400-meter runner who made the quarter finals of the men's race in 1988 and the same year ran in the finals as a member of the 4x400m relay. Sang was a member of the Kalenjin tribe that has clashed with Kikuyus.