Bahrain security forces have attacked the headquarters of the country's Shia opposition, the group says.Tear gas and rubber bullets were fired at protesters at its offices west of Manama, Al-Wefaq said.
More than 40 people died in a crackdown against protesters in Bahrain in the spring. An independent commission concluded "excessive force" was used.
The violence has fuelled anger against the Sunni ruling family and political elite in majority Shia Bahrain.
Al-Wefaq said that several people, including children, had been wounded in Friday's crackdown, which reports said happened after opposition supporters attempted to defy a government ban on demonstrations.
"We are a people that won't be broken. All this repression and brutality is the source of our strength and determination to continue the struggle and defend our national rights," Al-Wefaq's vice-president, Sheikh Hassan Al Daihi, said in a statement.
According to the Associated Press, Shia clerics also held prayer services on Friday on the rubble of mosques that had been bulldozed by authorities earlier this year.
"We will start a campaign to defend our religious sites and the first such activity starts with a protest at the end of the prayer at Diraz grand mosque," senior Shia cleric Sheik Isa Qassim said during his Friday sermon, the news agency reports.
Diraz is an opposition stronghold north-west of the capital.
More than 1,600 people have been arrested during the protests this year in Bahrain, which have continued sporadically since the peak of the unrest eight months ago.