NAIROBI, Kenya (CNN) -- Tear gas was fired Wednesday on people taking part in a prayer march sparking more post-election violence in the Kenyan capital.
Marchers threw stones at cars and office buildings, and some vehicles and buildings were set on fire.
Supporters of the opposition Orange Democratic Movement (ODM) and its candidate, Raila Odinga, have been protesting the outcome of the December presidential elections that saw incumbent Mwai Kibaki keep his post.
Odinga and his supporters claim the election was rigged, and international observers noted some irregularities with the voting.
A statement from the police commissioner said: "Immediately after the prayers ended, part of the crowd used petrol bombs to set fire to the nearby post office building causing extensive damage to property," said .
"Were it not for swift action by police and the city fire brigade, this premeditated criminal act could have caused the death of the innocent Kenyans who were locked inside the building before it was set on fire."
Police said the march was authorized only after ODM leaders promised it would be peaceful.
More than 500 people have died in the violence following the election.
Prayer meetings planned for Thursday and Friday have now been banned, police said. But ODM spokesman Salim Lone told CNN the protests were canceled by the ODM at the request of Kofi Annan.
The former U.N. secretary-general met Wednesday with Odinga and his ally, Kenneth Marende. He is scheduled to meet with President Mwai Kibaki Thursday morning, according to the African Press Agency.
Marende, the speaker in Kenya's parliament, told reporters Annan would push for a meeting between Odinga and Kibaki.
"We have addressed issues that are pertinent, and I think it is a good start," he said.
Annan's talks with Odinga were expected to go far into the night.
Kenyan Foreign Minister Moses Wetang'ula said Monday it is hoped Annan will start a dialogue to help resolve the crisis, but pointed out that only Kenya's courts can decide if Kibaki's government is legitimate. E-mail to a friend