NAIROBI — Tensions were on the rise in western Kenya and parts of Nairobi amid confusion and discrepancies surrounding the country’s repeated presidential election this past week, with deadly violence breaking out in some areas.

Shops were burned Friday night in Kawangware, a neighborhood in central Nairobi, and a civil society group reported that six people had been injured, including three with machete wounds. The neighborhood is a stronghold of the opposition leader Raila Odinga, who withdrew from the presidential race two weeks before the second vote.

In western Kenya, where Mr. Odinga enjoys strong support, demonstrators clashed with the police. Six people were killed, 13 injured and 86 arrested in election-related unrest nationally, the police said late Friday.

Mr. Odinga lost to President Uhuru Kenyatta in the first vote, in August, but challenged the validity of the results. The Supreme Court, citing irregularities and possible hacking, called for a new election by the end of October.