Former U.N. Secretary-General Kofi Annan has arrived in Kenya to try to end a violent political crisis that has killed more than 650 people.

Mr. Annan will try to forge an agreement between President Mwai Kibaki and opposition leader Raila Odinga, who accuses Mr. Kibaki of stealing last month's presidential election.

Reports from western Kenya say at least seven more people died Tuesday in tribal violence set off by the election.  The reports say four of the victims were hacked to death in Rift Valley province.

Earlier, Kenya's government and main opposition threatened to file complaints against each other with the International Criminal Court in the Hague.

Mr. Odinga's Orange Democratic Movement (ODM) said authorities committed crimes against humanity when police fired on civilians during recent protests.  The government accused the opposition of planning ethnic cleansing in the Rift Valley.

Mr. Odinga's supporters are planning to hold another protest on Thursday despite a police ban on street protests.  Earlier today, police fired tear gas to disperse about 100 pro-Kibaki supporters in Nairobi ahead of Mr. Annan's arrival.

Ugandan President Yoweri Museveni is also taking part in mediation efforts and met with Mr. Kibaki in Nairobi today.

In another development, the U.S. ambassador to Kenya has denounced print and broadcast advertisements placed by Mr. Kibaki's government accusing the U.S. and other Western countries of helping to incite the violence.

In an editorial published in Nairobi's Daily Nation newspaper Tuesday, Ambassador Michael Rannenberger said the ads were "scurrilous propaganda."
The editorial follows another diplomatic dispute between Kenya and Britain.  On Monday, the Kibaki government summoned the British High Commissioner to protest remarks by British lawmakers that London does not recognize Mr. Kibaki as the winner of the election.

Some information for this report was provided by AFP, AP and Reuters.