Fierce fighting over land killed 22 people and left 200 homes burned in Kenya's troubled western Rift Valley, officials said Sunday, yet another eruption of ethnic clashes following the disputed re-election of President Mwai Kibaki.

Renewed ethnic fighting also broke out in Nairobi's Mathare slum Sunday, where several homes were set ablaze during several hours of running battles between Kikuyu and Luo ethnic groups, said resident Boniface Shikami.

President Mwai Kibaki is Kikuyu and opposition leader Raila Odinga, who charges Kibaki stole the Dec. 27 election, is a Luo.

An Associated Press reporter saw the body of one man who was beaten to death in Mathare — a Luo who was riding his bicycle through a group of Kikuyus. Another staggered past, blood streaming from the stump of his arm which had been cut off with a machete. The arm was taken by a group of youths and placed on top of a pile of stones barricading an alleyway.

Resident Moses Ogolla said he saw four bodies being put into a police vehicle that morning with deep machete cuts. "I think it was a gang who attacked them because some bodies, the head had six, seven, eight cuts on it," he said. Ogolla said that he believed the victims were Luo because he heard the families conversing in the Luo language.

"The Luo guys say they are going to revenge this," he said.

Shikami said Luos in his street had received notices warning them to leave by nightfall or risk attack. Filipe Rebeiro of aid group Medecins Sans Frontieres, or Doctors Without Borders, said his organization had treated 10 people for machete and ax wounds on Sunday morning.

In the Rift Valley, around the Catholic Kipkelion Monastery about 190 miles northwest of Nairobi, Kalenjin people native to the area fought Kisii and Kikuyu settlers with machetes, swords and bows and arrows. The Kalenjin generally support the opposition party.

A local reporter at the scene saw 17 people who had died from machete and arrow wounds and five shot by police, who appeared to have quelled the violence by early Sunday afternoon but still were recovering bodies.

The death toll also was confirmed by district administrator Aden Alhake

Edward Ndirangu, who said two of his houses were razed, was searching for his wife and three children. "I am not sure about their safety. ... We fled as they were looting and torched my homes," he said.

He was among 2,500 Kikuyus and Kisii who have sought refuge at three schools and the monastery, which was being protected by police.

On Saturday, Kenya's opposition party, determined to bring down the Kibaki's government called for another day of "peaceful rallies" across Kenya in defiance of a ban and despite the deaths of at least 24 people in last week's demonstrations — all but seven deaths blamed on police.

Police took forceful action at rallies Wednesday through Friday protesting the Dec. 27 presidential election, but opposition party chairman Henry Kosgey told reporters on Saturday, "We will use each and every means to bring down Kibaki's government."

Despite the deaths, Kosgey called for more rallies on Thursday, to the disapproval of the European Union.

"Mass meetings ... can lead to violence," EU Development Commissioner Louis Michel said, after holding what he called "positive" meetings with both Kibaki Odinga. He said both sides "appeal to end the violence," and had agreed to recognize mediation efforts by former U.N. Secretary-General Kofi Annan.

More than 600 people have been killed in Kenya's election violence, according to a government commission.

U.S. Ambassador Michael Ranneberger said Friday there had been "a lot of cheating on both sides" in the elections.

Ranneberger said either Odinga or Kibaki could have won by 120,000 votes because it was a close election that both sides are alleged to have rigged. David Throup, an associate of the Washington D.C.-based Center for Strategic and International Studies, said in a public conference call with Ranneberger that Odinga won by 120,000 votes.

But Kibaki's power becomes more entrenched each day. The opposition's best hope may rest in wrangling a power-sharing agreement that might make Odinga prime minister or vice president.

International mediation continued. A group of former African presidents — Tanzania's Benjamin Mkapa, Mozambique's Joachim Chissano and Botswana's Ketumile Masire — met with both Odinga and Kibaki, Odinga told reporters after the meeting Friday.

Annan, the former U.N. chief, is expected Tuesday to head mediation efforts, his office in Geneva said.

Michel, the EU development commissioner, met Saturday with Deputy President Kalonzo Musyoka, and urged him to come to an agreement with the opposition "because the consequence of chaos will be so important and so badly affect the people and the region."

Kalonzo said, "We are trying to come out with a healing process and a process which also ensures we engage each other as Kenyans in dialogue." He said Kibaki was determined to spearhead the dialogue.

But Kibaki has said he wants direct talks with Odinga, while the opposition leader says he will negotiate only through a mediator who can provide an internationally guaranteed agreement. Odinga had previously supported Kibaki in the 2002 election in return for a promised prime ministership, which failed to materialize.

European Parliament legislators last week urged aid cuts to help force Kibaki to negotiate. His government says it will not be blackmailed but the violence has cost the tourist-dependent economy at least $1 billion, the Finance Ministry has said.