Both Ambassador Chris Hill and other embassy personnel were unhurt in the explosion, which occurred when the convoy was driving through the province. The incident was being investigated, said the embassy.

The blast came just two weeks after US combat forces completely withdrew from Iraqi urban areas.

CNN reports that Thiqar province, which is dominated by Shiites, was one of the first areas handed over to Iraqi security forces, and saw periodic clashes between Iraqi forces and insurgents loyal to Shiite cleric Muqtada al-Sadr in 2007.