Street protests spread through towns across Senegal overnight on Saturday after a top legal body said President Abdoulaye Wade had the right to run for a third term in elections next month.
Local television said one policeman died from head injuries after clashes in the capital Dakar. Reuters reporters saw youths set fire to tires and overturn cars after a ruling of the West African country's Constitutional Council late on Friday night.
Rivals to 85-year-old Wade say the constitution sets an upper limit of two terms on the president. Wade, who came to power in 2000 and was re-elected in 2007, has argued his first term pre-dated the 2001 amendment establishing the limit.
Senegal's Constitutional Council validated his candidacy and that of 13 rivals for the Feb. 26 vote but turned down the presidential bid of world music star Youssou N'Dour, saying he had not gathered the required 10,000 signatures of support.
N'Dour called on his supporters to prevent the elections from going ahead.
"We will never allow Abdoulaye Wade to take part in the election," he said, speaking on his own TFM television channel.
"The decision to keep me out had nothing to do with the law. It was a political decision and we will reply with a political decision," he said, without giving further details.
Senegal is the only country in mainland West Africa to have not had a coup since the end of the colonial era. February's poll, and a possible run-off a few weeks later, are seen as major test of social peace in the predominantly Muslim country.
One witness said a police station in the central town of Kaolack had been ransacked, while state radio said the local headquarters of Wade's liberal PDS had been burned down. Street protests were also reported in the towns of Thies and Mbour.
"Wade has no right to a third term and the people will resist this," Moustapha Niasse, a former prime minister for Wade who is now challenging him for the presidency, said.
Wade appeared on state television and made an appeal for calm, promising that the elections would be free and fair.
"Stop these displays of petulance which will lead to nothing," he said. "The electoral campaign will be open. There will be no restrictions on freedom."
The Council validated 13 other candidates including Socialist Party leader Ousmane Tanor Dieng, Niasse and two other ex-prime ministers - Idrissa Seck and Macky Sall.
Its five judges, all selected by Wade, said authorities had been unable to identify around 4,000 of some 12,000 signatures gathered by N'Dour, meaning his candidacy was invalid.
"We are here to protest against Wade," Yero Toure, a 26-year-old student at an opposition rally of a couple of thousand people in central Dakar before the ruling. "If they don't reject him the people will rise up against him."
Critics say that Wade, who spent 26 years in opposition to Socialist rule, has done nothing during his 12 years in power to alleviate poverty in a country where formal employment is scarce, and has dragged his heels on tackling official graft.
Wade points to spending on education and infrastructure projects such as roadbuilding as proof of progress towards turning Senegal into an emerging market country and a trade hub.
His candidacy has raised eyebrows abroad. The senior U.S. State Department official for Africa, William Fitzgerald, told French RFI radio this month Washington viewed it as "a bit regrettable".
"From our point of view it was the right moment to go into retirement, to protect and support a good transition - democratically, peacefully, safely," Fitzgerald said.