Demonstrators clashed with police outside Senegal's National Assembly on Thursday as they protested against a constitutional amendment changing the rules of presidential elections.

Stones and other missiles were hurled at police, who retaliated with teargas and jets of heated water from water cannons, reports Agence de Presse Sénégalaise from Dakar. Riot police were called in to help push back the crowd. A police vehicle was destroyed.

Police sources said opposition members and supporters besieged the parliamentary precincts early Thursday morning, chanting anti-government slogans and denouncing any form of constitutional amendment.

The protests were joined by youths and and civil society activists, among whom spontaneous demonstrations erupted after the constitutional amendments were announced on Monday.

Also on Monday, opposition political leaders met and resolved to block a change which would see presidential aspirants run on a combined ticket with a vice-presidential candidate.

Another amendment provided that a presidential and vice-presidential candidate could be declared the first-round winners with only 25 percent of votes.

A coalition of opposition parties vowed that even if parliament approves the amendments, they will make sure the changes come into effect only after forthcoming elections.

** Later on Thursday President Abdoulaye Wade retracted the amendment allowing the election of a candidate who wins 25 percent of votes.