A bomb placed under a vehicle exploded near the British embassy in Bahrain's capital Manama but caused no casualties, according to the Gulf Arab state's interior ministry and embassy officials.

"Given the strength of the explosion and the debris it scattered, it was a highly explosive substance that was used," a ministry spokesperson said in comments on Twitter posted live from a news conference.

"The explosion was the result of a package placed under the front tyre," he said, adding there were no casualties. He described the vehicle as a minibus parked some 50m from the embassy compound early on Sunday.

Bahrain has been tense since pro-democracy protests erupted in February following revolts in Egypt and Tunisia. The government imposed martial law for nearly three months and ordered mass detentions and trials to crush the protests.

The government, dominated by the Sunni Muslim al-Khalifa family, said the protests, led by majority Shia, had sectarian motives.

"We are working with the Interior Ministry and we have requested a temporary increase in security," a spokesperson at the British embassy said, adding the blast took place between 1 and 2am.

"There were no casualties or damage to the embassy. We cannot identify yet the cause or the responsibility."

Source: Agencies