Senegalese police have fired tear gas on marchers in Dakar protesting proposed changes to election laws that opponents say would make it easier for the president to be re-elected.

Witnesses say the demonstrators were throwing stones at the parliament building when the altercation began Thursday.

VOA's correspondent in Dakar said Wednesday protestors destroyed a bus near the Place de Independence, a large square in the capital. He says riot police broke up the demonstrations with tear gas and says officers are posted throughout the city.

Reports from Senegal say there were also protests in the Dakar suburb of Pikine, and the central city of Kaolack.

Senegal's National Assembly is to vote Thursday on a law proposed by the ruling party that would lower the percentage of votes a winning candidate needs to avoid an election runoff. Opponents say the change would favor Senegal's incumbent President Abdoulaye Wade.

The proposed law would also create a new post of vice president, which opponents believe is intended for Mr. Wade's son.

The U.S. embassy in Dakar warned Americans in the city about more demonstrations on Thursday. It urged U.S. citizens to avoid crowds, saying the protests could quickly turn violent.