Riot police have used tear gas and water cannon to disperse protesters on the streets of Kenya's capital, Nairobi. The rally has been organised by opposition leader Raila Odinga to protest against the controversial re-election of President Mwai Kibaki. Odinga hopes to attract a million supporters to the rally, which has been banned by the government. As Bernard Smith reports for Al Jazeera, the streets of Nairobi are extremely tense, with fears of violent clashes between protesters and police.