The bodies of three men and a woman were found in the city's Mathare slum, one of several flashpoint areas where violence erupted during last month's disputed presidential election re-run, which was largely boycotted by the opposition.
It was not immediately clear how they had died, but the discovery fanned tensions, coming just days after three people were shot dead by police in a nearby suburb as thousands of opposition supporters turned out in support of their leader, Raila Odinga.
He said angry residents, who claimed the violence was ethnically driven, had set fire to two buses and another vehicle, with police sealing off the area.
Locals blamed the deaths on the Mungiki, a feared gang known for running protection rackets and violently defending tribal business interests.
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Its members come from the Kikuyu tribe of President Uhuru Kenyatta, and many of them live in the Mathare slum alongside ethnic Luo or Luhya, who largely back Odinga.
Although Kenyatta won the October 26 vote with 98 per cent of the votes cast, the ballot was boycotted by Odinga and marred by low turnout and violent protests.
The vote was the chaotic climax of two months of political drama after the Supreme Court overturned Kenyatta's victory in an initial August 8 poll over widespread irregularities and mismanagement by the IEBC.
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