|The presence on Iraqi streets of US troops, pictured on patrol in Basra in 2010, is increasingly rare [US Army]
Six people have been killed in Basra, southern Iraq, after a civilian bus was blown up in a roadside bomb attack on a US military convoy, according to local officials.
At least 12 people, mostly civilian, were injured by the blast, Ali al-Maliki, the head of the Basra provincial council's security committee, told the Reuters news agency. Women and children were among the casualties he said.
Reuters television footage showed US troops and Iraqi security forces surrounding the scene of the bombing.
Ahmed Hamid, Basra's deputy governor said the blast occurred near a prison in the al-Maaqal district of northern Basra.
"A roadside bomb exploded near a civilian bus," Hamid said. "Most of the casualties are civilian. The explosion happened near the prison and was targeting a U.S. patrol."
Violence has fallen sharply in Iraq since 2007 but almost 200 people died as a result of violence in February, according to the Agence-France Presse news agency.
The presence of US troops on the streets is increasingly rare. Some 50,000 soldiers are still stationed in the country but mainly to assist with training Iraqi security forces. All forces are due to leave by the end of the year.