A court jailed nine Bahrainis for life on Monday for forming a militant group, manufacturing explosives and plotting attacks aimed at destabilising the kingdom, state news agency BNA reported.

The trial was the latest in a series involving alleged anti-government activists in the Gulf Arab state, still beset by political tensions more than two years after security forces quelled pro-democracy protests led by Shia Muslims.

BNA said the convicted men had turned a Manama warehouse into a bomb factory, where they had prepared explosives to attack security forces, civilians and private and public property "with the aim of undermining the stability of the country and harming its economic foundations".

Pro-democracy protests erupted in 2011, led by majority Shia demanding an end to the Sunni monarchy's political domination of Bahrain, which hosts the U.S. Navy's Fifth Fleet.

Bahrain accuses Shia Iran of fuelling the unrest, something Tehran denies, and says it is fighting terrorists. In July, a homemade bomb killed a policeman in a northern village.

BNA said that four of those convicted in the case, which dates back to 2012, were in custody, suggesting that the other five are at large. It said some were behind a November 2011 bombing that damaged cars near the country's exhibition centre.