Senegal's opposition has called for fresh protests on Monday in the capital Dakar ahead of a controversial presidential vote on February 26.
"We call for a protest at 3:00 pm (1500GMT) at Independence Square," Alioune Tine, co-ordinator of the June 23 Movement (M23) of opposition and civil society, said.
Several days of protests against the planned vote in which President Abdoulaye Wade is seeking a third term has claimed two lives.
Demonstrations against the 85-year-old president's attempt to extend his rule have intensified in Dakar, as protesters seized control of a three-block stretch in the heart of the city on Sunday, erecting barricades and lobbing rocks at the police.
Senegal's state broadcaster reported that at least two persons were killed during Sunday's violence.
The clashes on Sunday marked a worrying development, as violence took on a religious dimension in the normally tolerant Muslim-majority country.
Hundreds had gathered outside a mosque as religious leaders met to discuss an incident which occurred on Friday, in which police used grenade launchers to throw tear gas down the wide boulevard, at one point hitting the wall of the mosque.
Footage of the incident shown on Senegalese TV indicated that the police had not shot inside the mosque, only outside where a crowd had gathered. But the cloud of gas enveloped worshippers praying both inside and outside the
place of worship, deeply offending the influential Muslim group that owns the mosque.
On Sunday morning, as a crowd outside the mosque grew, a truck of riot police took up a defensive position at one end of Lamine Gueye boulevard, and the dozens of youths erupted in jeers.
They then grabbed cinderblocks from a nearby construction site and hurled them at police. Security forces responded with volleys of tear gas.
The clash continued for several hours, until protesters succeeded in seizing control of a three-block stretch of the road, one of the main commercial roads in downtown Dakar.
They grabbed market tables and pieces of plywood that had been nailed across shop windows, using them as shields to
protect themselves from the tear gas grenades. They then lined them across the road's median, as police were momentarily pushed back, waiting for reinforcements.
Some protesters also set fire to tires and smashed car windows, while witnesses reported that the police had fired rubber bullets in addition to tear gas.
Each time the youths charged the police, they screamed, "God is great" and "There is no God but Allah", religious phrases that are rarely heard in this nation that is over 90 per cent Muslim but which has long embraced a
"I'm worried, yes. What I'm seeing here could really degenerate into another kind of situation, a religious one," said Moustapha Faye, a young member of the Mouride Muslim brotherhood, the second largest in Senegal, as he stood behind the police line watching the confrontation. "We must absolutely avoid violence."
Later on Sunday, Ousmane Ngom, the interior minister, apologised to the nation, calling Friday's attack on the mosque a "police blunder". During the broadcast on state television, Ngom asked for the forgiveness of the Tidiane community and all Muslims, while calling on politicians not to exploit the incident for political gain.
The protests in downtown Dakar spread to numerous neighbourhoods, including HLM, Parcelles, Castor and Rufisque.
The increasingly tense atmosphere on the ground has many concerned that there may be worse unrest if Wade is declared the winner of next Sunday's vote.
Wade has been in power for 12 years, but in 2001 he oversaw a revision of the constitution that imposed a two-term maximum on presidents. He argues that the new constitution is not retroactive, and hence he is still eligible to run in next week's election.
Protests erupted in January when the country's highest court ruled in his favour in a case regarding his eligibility.