ABU DHABI: Seven Bahrainis have been detained over clashes that killed a policeman, Bahrain's government said on Sunday, as activists tried to break through police checkpoints around the village where he died.

The Gulf Arab kingdom has been convulsed by unrest since February last year after mass demonstrations led by majority Shi'ites demanding democratic change in the Sunni-led monarchy.

The ruling Al Khalifa family brought in Gulf Arab troops, mainly from Saudi Arabia, and imposed over two months of martial law to end the uprising.

The incident in the early hours of Friday was the first in which a policeman had been killed since martial law ended in June 2011. Policemen were attacked by rioters with petrol bombs and an unspecified "explosive device", the authorities said.

"Seven Bahrainis have been detained and have been referred to the public prosecution in the case of a bombing attack in al-Eker ... in which one policeman was killed and a second critically wounded during a routine patrol," a statement from the government's Information Affairs Authority said.

It named the dead policeman as 19-year-old Imran Ahmed. It did not give his nationality. Many Pakistanis and some Arab nationals serve in Bahrain's riot police - a source of friction with protesters.

The opposition, who say more than 45 people have died in clashes since martial law ended, want full legislative powers for parliament and parliament approval of cabinet, which has been headed by an uncle of King Hamad bin Isa since 1971.

Wefaq, the main opposition group in Bahrain, said on Sunday that clashes had broken out near al-Eker, south of Manama, after some rights activists and medics tried to enter the village, which police has blocked off since Friday.

"Al-Eker is still under siege and nobody is allowed in or out, even cars carrying food supplies are prevented from reaching people there," Wefaq said in a statement.

The government statement said checkpoints had been set up as part of efforts to find those behind Ahmed's death. "The security measures put in place in al-Eker in the form of checkpoints at the entrances of the area are aimed at verifying the IDs of those entering and leaving the village," it said.

The United States, which moors its Fifth Fleet in Manama, has backed the government throughout the unrest but called for dialogue with the opposition.

The fleet would be key to maintaining oil shipments out of the Gulf if the United States' conflict with Iran over its nuclear energy programme leads to military confrontation.

Bahrain's government has depicted the opposition as an Iran-backed movement with Shi'ite sectarian motives. Iran and protesters say this is an excuse to avoid reforms.

Shi'ites complain of discrimination in the electoral system, jobs, housing and education, which the government denies.