Gen Tariq al-Hassan said an improvised explosive device was detonated near a police checkpoint late on Monday.
Three of the policemen were injured critically by the blast, he added.
Bomb attacks are rare in Bahrain, despite frequent clashes between security forces in the Wahabi ruled kingdom and protesters from its Shia majority.
The main Shia opposition group, al-Wefaq, said Akr had been “entirely surrounded by security forces who are imposing collective punishment”.
“We have received calls for help from village residents,” it said in a statement, adding that police had also been firing “pellet guns” at them.
The interior ministry said protesters had thrown petrol bombs at the policemen to lure them into the predominantly Shia village, which lies to the south of the capital Manama, before the bomb was detonated.
Gen Hassan said an initial investigation revealed that the explosion was caused by a “pipe bomb attached to a container full of gasoline”.
An underground group calling themselves the 14 February Youth Coalition – after the date when mass pro-democracy protests erupted last year – has threatened to carry out attacks with “holy petrol bombs” and launch “martyrdom ambushes”, according to the Reuters news agency.
Anti-government demonstrations have increased in the recent weeks as tensions have risen over the worsening condition of a human rights activist who has been on hunger strike in prison for 62 days.
Abdulhadi al-Khawaja has refused food since 8 February, in protest at the life sentence he received from a military court in June for allegedly plotting against the state, and is said to be at risk of death.
At least 80 people have been killed in Bahrain since February 2011, according to the International Federation for Human Rights, when Shia-dominated protests rocked the streets of Manama.
Despite a heavy-handed crackdown in March 2011, backed by Saudi-led Gulf troops, demonstrators were soon back on the street.
A national dialogue was relaunched in February with the aim of resolving the political deadlock in the country.
- Al Khalifa’s Saudi Backed Bahraini forces lay siege to a Shia Majority Village to Terrorize (jafrianews.com)
- Saudi Backed Bahriani Forces Raided the House of the Top Shia Cleric to enrage the Shiite Population (jafrianews.com)
- Thousands of Bahraini Shia Stages a Sit In , to Protest the Raid on Bahrain’s Top Shia Cleric’s home (jafrianews.com)