One man was shot and killed in Guinea's capital Conakry on Monday at the start of open-ended protests against President Alpha Conde.
The West African country has been wracked by demonstrations since mid-October over concerns Conde intends to use a planned constitutional reform to extend his mandate.
At least 20 civilians and one gendarme have been killed since the start of protests, which have drawn hundreds of thousands of people while scores have been arrested.
Scuffles broke out on Monday between young people and the police, an AFP journalist said.
A student Elhadj Mamadou Sow, 21, was killed in the unrest, according to his uncle, who declined to be named.
The uncle said he was shot by a security officer who was chasing a group of young people.
"We heard gun fire -- pah, pah, pah, -- and suddenly we heard screams and all the young people gathered around my nephew who was on the ground, wounded in the chest," he added.
A doctor confirmed that Mamadou Sow had died and told AFP he was shot at close range.
Amadou Camara, the spokesperson for Guinea's national police, said the police would investigate.
After months of organising mass protests, the National Front for the Defence of the Constitution (FNDC), an alliance of opposition groups, raised the stakes last week and called for "huge" and "open-ended" demonstrations.
The political opposition is convinced that Conde put forward a draft constitution last month intending to keep himself in office for a third term.
Conde, 81, has neither confirmed nor denied that claim but has argued that the colonial-era constitution needs to be changed.
The current constitution in the former French colony stipulates two presidential terms.
The government on Sunday accused opposition leaders of seeking to plunge Guinea into disorder. The FNDC had called for a peaceful protest.
Guinea's Security Minister Albert Damantang Camara also said on Monday that he has "the manpower, methods and capabilities" to intervene whenever necessary.
Shops and schools were shut across Conakry on Monday, an AFP journalist said, while streets were mostly empty of traffic.
"The FNDC's call for resistance is being widely followed in several cities in Guinea," the opposition group said in a statement.
"This has resulted in a total paralysis of the main roads, the closure of shops and businesses," it added.
The FNDC also confirmed that there had been clashes in Conakry, and in the cities Boffa and N'Zerekore.
Abdourahmane Sanoh, the group's spokesman, told AFP the start of the protest had been "a success".