NAIROBI, Kenya — Post-election attacks on villagers in Kenya’s western Rift Valley were often “meticulously” organized by local opposition leaders who called for “war” against people from President Mwai Kibaki’s Kikuyu tribe, according to a report by the group Human Rights Watch released yesterday.

The report also detailed widespread killings by Kenyan police of opposition supporters, especially in the opposition stronghold of Kisumu in western Kenya. It also found circumstantial evidence to suggest that senior government officials were aware of planned reprisal attacks by Kikuyu gangs against opposition supporters in several other western towns.

A prominent Kenyan diplomat told the Washington Post that it was an “open secret” that certain Kikuyu politicians provided funding for gangs of young Kikuyu men and ferried them to the town of Naivasha, where they helped carry out one of the most brutal revenge attacks in late January.

“This was not done by ordinary citizens, it was arranged by people with money,” one young man who took part in the attacks said, according to the report. “They brought the jobless like me. We need something to eat each day.” Violence following Kenya’s disputed December 27 presidential elections is estimated to have killed at least 1,000 people and displaced more than 500,000, with most of the violence taking place across the volatile Rift Valley, where long-standing grievances over land fueled much of the violence.

The violence tarred Kenya’s image as one of Africa’s political success stories, rekindling tribal animosities and controversy over land use and government corruption. After weeks of international negotiation, leaders reached an agreement meant to defuse the crisis.