DUBAI: An interior ministry bus was attacked in Bahrain on Friday, state news agency BNA reported, as the opposition reported the arrest of a woman member trying to travel abroad for an Amnesty International conference.

"A group of rioters and saboteurs attacked the bus with Molotov cocktail bombs" near the Shiite village of Bani Jamra, BNA quoted a police official as saying.

The agency said the driver and a companion were unhurt but the bus was gutted.

"Police have launched an inquiry to identify the perpetrators and bring them to justice," the official was quoted as saying.

Witnesses said protesters and police clashed in several Shiite villages late on Thursday and early on Friday.

Dozens of people chanted "Down with (King) Hamad" and "The people want to overthrow the regime," as they waved the kingdom's red and white flag, they said.

Security forces fired tear gas and birdshot, the witnesses said, adding that several people were wounded.

The authorities accuse Shiite protesters of using petrol bombs against security forces during frequent demonstrations in villages outside the capital Manama.

Sporadic protests have intensified since a March 2011 crackdown ended month-long protests in Manama's main Pearl Square demanding democratic reforms in the Sunni-ruled Shiite-majority Gulf state.

The main Shiite opposition bloc Al-Wefaq said the authorities detained a leading female member, Ahlam al-Khuzai, at the airport early on Friday.

Khuzai was arrested as she was travelling to Tunisia for a conference organised by London-based rights watchdog Amnesty International, Al-Wefaq said in a statement.

"Al-Wefaq is following with great concern the arrest of its general secretariat member Khuzai... She is still in custody," it said.

Al-Wefaq has said more than 240 people were arrested in July, and dozens were injured in clashes with the police.

Amnesty says 60 people have been killed since the protests first erupted in February last year.