Guinea police have fired tear gas to disperse protesters angry at the government's handling of overdue parliamentary elections.
Thousands of opposition supporters rallied in the capital Conakry, with a number reported injured after clashes with the police.
Elections should have been held within six months of President Alpha Conde's inauguration in December 2010.
The opposition say Mr Conde is trying to rig the polls.
Protesters also called for an overhaul of the electoral commission, Ceni, saying it is biased towards the ruling party.
In April, President Conde postponed parliamentary elections, which were due to be held in July, saying technical problems with the voter registration system needed to be fixed.
A transitional council served as a parliament since 2010, during the country's transition from military to civilian rule.
The European Union, a major donor to Guinea, has warned it will not unlock millions of dollars of suspended foreign aid until legislative elections are held.
The BBC's Alhassan Sillah in Conakry says clashes broke out when police fired tear gas at youths - and when opposition supporters threw stones at the ruling party headquarters.
He says that at one hospital he saw a handful of opposition supporters being treated for bayonet injuries.
Our correspondent also visited an opposition stronghold in a Conakry suburb, where tyres had been set on fire.
He says the violence was not as much as some protests in Guinea, which have ended in widespread bloodshed.
In 2009, at least 157 people protesting against the then-military junta of Moussa Dadis Camara died when the troops opened fire in a Conakry stadium, and 100 women were raped.
The last legislative elections were held in June 2002 during the regime of President Lansana Conte, who died in December 2008 after 24 years in power.