At least one person was killed on Tuesday as Senegalese security forces armed with truncheons and tear gas clashed with rock-throwing activists protesting against President Abdoulaye Wade's decision to seek a third term.
A 30-year-old student was run over by a truck and died from his injuries after mass protests in the capital Dakar turned violent, a government official, who asked not to be named, told Reuters.
Senegal's top legal body, the Constitutional Council, confirmed on Monday that Wade, 85, could stand for re-election, despite complaints it breached rules setting a two-term limit.
The ruling provoked protests across Senegal - long seen as haven of stability in West Africa. The United States said on Monday Wade's decision to seek a third term could endanger the country's record of democracy.
Opposition leaders and thousands of activists, brought together by the umbrella M23 campaign group, gathered in central Dakar on Tuesday calling on Wade to reconsider his decision to run in the Feb. 26 election.
Some of the protesters hurled stones at police who retaliated with truncheons and tear gas, a Reuters reporter at the scene said.
"Wade leave now. The people are fed up," protesters chanted in footage broadcast by TFM, a television station owned by world music star Youssou N'Dour, whose presidential bid was rejected by the Constitutional Council.
M23 leaders have called the ruling a "constitutional coup" and threatened to make the country ungovernable.
"When we talk of a coup we think about the military. But a civilian coup is much harder because it's something that we do not see but we experience it," N'Dour told a news conference before addressing the protest on Tuesday.
Wade, who was re-elected in 2007, has argued his first term should not be counted in a two-term limit added to the constitution in 2001. The five judges of the Constitutional Council - all picked by him - agreed with that interpretation.
Several opposition candidates who have been cleared to run in the vote, took part in the protest rally and called on Wade to withdraw his bid.
Four people have been killed across the country since anti-Wade demonstrations began on Friday.
A woman and a 17-year-old student were killed during a protest in Podor, a town on the border with Mauritania, on Monday. A policeman was killed during riots in the capital on Friday.
The United Nations on Tuesday urged all sides to refrain from violence.
"(U.N. Secretary-General Ban Ki-moon) is concerned about the upsurge of tensions in Senegal," it said in a statement.
Alioune Tine, president of rights group RADDHO and M23 coordinator, told local Radio RFM that the only way to ease the tension in the country was for Wade to withdraw his candidacy.
"Wade needs to be told the truth. He must retire to preserve peace and security," Tine said.
High youth unemployment and rolling power cuts have added to tensions in the country in the past months.