DUBAI, United Arab Emirates — A remotely detonated bomb injured at least seven policemen on patrol in Bahrain on Wednesday, a security source said.

"There was an ambush . . . while they [the police] were working on unblocking roads, they were targeted and three of them are seriously wounded," the source said.

At least four other policemen were less seriously hurt in the attack in Bani Jamra village, west of the capital Manama, where youths have regularly blocked roads and clashed with police in recent months.

Police say they have been frequently attacked with homemade bombs since April 2012.

The majority Shiite country, ruled by the Sunni al-Khalifa family, has been buffeted by political turmoil since 2011 when protesters, mostly Shiite, took to the streets calling for democratic reforms and more say in government.

The Bahraini government has largely crushed the revolt but small-scale protests erupt almost daily.

Tensions have been especially high since security forces raided a top Shi'ite cleric's home on May 17.

Hundreds of Shiites clashed with police last Friday, and thousands more gathered in the cleric's village for a peaceful sit-in.