NAIROBI, Kenya — A solution to the dispute about the presidential election must be found “for the sake of Kenya and its people and for the sake of Africa,” the former chief of the United Nations said yesterday.

Kofi Annan, the former U.N. Secretary-General, will try to bring President Kibaki and his main challenger, Raila Odinga, together after the December 27 election that foreign observers say was deeply flawed.

Hours earlier, the opposition accused the government of “crimes against humanity” and said it would file a complaint with the International Criminal Court in the Hague.

Both sides have traded accusations of who is behind the post-election violence, and each side has accused the other of “genocide.” The death toll has reached 685, the government said yesterday.

The election returned Mr. Kibaki to power for a second five-year term, with official results putting Mr. Odinga in second place. Mr. Odinga accused Mr. Kibaki of stealing the vote, and protests exploded into riots and ethnic fighting.

The election has tapped into resentments that resurface regularly at election time in Kenya. But never before has the anger been so prolonged or taken so many lives. Mr. Odinga has called for another “peaceful protest” tomorrow, saying “let them bring their guns and we will face them.”

The protest will take place in defiance of a ban and despite the deaths of at least 24 people in protests last week.

Meanwhile, a Kenyan marathon runner was fatally shot with an arrow, the second international athlete to die as Kenya struggles with an explosion of post-election chaos, the head of Athletics Kenya, the governing body for Kenyan sports, David Okeyo, said yesterday.

Wesly Ngetich, 34, won the Grandma’s Marathon in Duluth, Minn., in 2005 and 2007. He and at least a dozen other Kenyans withdrew from the Rock ‘n’ Roll Arizona Marathon and Half-Marathon because of the political strife in Kenya.