At least 21 people, including five members of the Guinean security forces, were wounded Thursday when violence broke out during an opposition march in Conakry, the government said.
"At least five members of the security forces were wounded, including one who was stabbed," a government statement said, adding that several vehicles were also set on fire.
Mamadou Alpha Barry, spokesman for the paramilitary gendarmerie, said two gendarmes and two policemen were in critical condition.
Opposition supporters in the troubled west African country were protesting against a decree that sets June 30 as the date for elections that have been repeatedly delayed since 2011.
They argue that the conditions for a free and fair ballot have yet to be met.
The violence erupted when the march veered off its authorised course, prompting the police to intervene with tear gas and water cannon.
Several such incidents, some of them deadly, have occurred in recent weeks, prompting the United Nations Security Council to urge both the government and the opposition to exercise restraint.
The last legislative elections in the country were held in 2002 under then president Lansana Conte who ruled the former French colony for 24 years until his death in December 2008, prompting a disastrous coup marked by extreme police brutality.