An explosion destroyed the golden dome of one of Iraq's holiest Shia shrines today in an attack the British foreign secretary, Jack Straw, condemned as a "criminal and sacrilegious" attempt to foment civil unrest.

The bomb attack on the al-Askari shrine in Samarra, north of Baghdad, early this morning provoked Shia demonstrations across Iraq, with militants attacking at least six Sunni Muslim mosques in the capital and two in Basra.

Mr Straw, who last night returned from a visit to Iraq, warned: "It is vital that all groups in Iraq and elsewhere show restraint at this sensitive time and avoid retaliation."