Bahraini authorities say an explosion has wounded four policemen during clashes in one of the anti-government strongholds in the Gulf kingdom.

The Interior Ministry says two of the injured policemen are in critical condition after the blast, which occurred late on Tuesday in the mostly Shia village of Diraz, west of the capital Manama.

Wednesday's statement described it as a "terrorist act" but gave no details about the explosion.

The level of violence has increased in recent weeks in Bahrain, where uprisings began last year.

At least 50 people have been killed in unrest since February 2011.

[Source: AP]