Four British soldiers and a Kuwaiti interpreter have been killed on Thursday in a roadside bomb attack in the Shia stronghold of Basra in southern Iraq, CNN reported.

They were killed by the two night-time blasts, which the British military described as a "serious incident". Another British soldier was badly injured.

Basra is only ten miles from the Iranian border, and Britain has accused Iranian agents of organising and funding attacks on coalition troops.

The attack came in a moment of high pressure as 15 UK troops and marines were captured two weeks ago in Iran. The soldiers returned home on Thursday.

"We must hold firm against elements of terror," Prime Minister Tony Blair said upon hearing the news.