A bomb placed under a vehicle exploded near the British embassy in Bahrain's capital Manama early on Sunday, but caused no casualties, the Gulf Arab state's Interior Ministry said.
Given the strength of the explosion and the debris it scattered, it was a highly explosive substance that was used, a ministry spokesman 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 50 metres (yards) from the embassy compound.
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 Shi'ites, had sectarian motives and were fomented by Shi'ite power Iran.
A government-sponsored fact-finding commission headed by international rights lawyers said last month there was no evidence of Iranian interference but Bahrain said there was incitement by Iranian media.
A diplomatic crisis between Iran and Britain deepened last week after youths stormed the British embassy in Tehran in protest against banking sanctions Britain imposed over Iran's nuclear energy programme.
London withdrew its diplomats from Tehran and expelled Iranian diplomats from Britain, and other European countries withdraw envoys from Tehran in support of Britain. Iran denies that its nuclear programme is aimed at developing nuclear weapons.
We are working with the Interior Ministry and we have requested a temporary increase in security, a spokesman at the British embassy said, adding the blast took place between 1 and 2 a.m. There were no casualties or damage to the embassy. We cannot identify yet the cause or the responsibility.
Dubai-based defence and security analyst Theodore Karasik said the blast could be the start of an escalation in the social conflict in Bahrain, where there are still almost daily clashes between Shi'ite protesters and riot police.
Shi'ites are marking the religious mourning rites of Ashura this week, commemorating the death of the Prophet Mohammad's grandson Hussein.
The timing is significant because it occurred during Ashura, Karasik said. What we might be seeing now is a cell or two that are being set up by disgruntled Bahraini Shi'ites who now use bombs to achieve their goals. It's a jump to a new level.
(Writing by Andrew Hammond Editing by Tim Pearce)