A roadside bomb has killed at least 16 people travelling on a bus in southern Iraq, reports say.
Anti-US insurgents have often targeted pilgrims to Shia holy sites
At least 22 people were also wounded in the attack.
The civilian passenger bus was travelling on the Basra-Nasiriya road some 80km (50 miles) south of Nasiriya, police said.
The attack came a day after eight US soldiers and an interpreter were killed in two separate incidents, the US military said.
One attack took place in Diyala province, killing three soldiers and an interpreter, while five other soldiers were killed in a suicide attack in Baghdad.
Nasser al-Jabery, provincial head of police operations in Nasiriya, said the bus was carrying pilgrims from the Shia holy city of Najaf to Basra.
Earlier on Tuesday, police said four policemen, four insurgents and a civilian had been killed in a gun battle in the northern city of Mosul.
Also on Tuesday, talks have started between US and Iraqi officials on the future of the US military presence in Iraq.
"The two parties started today, in the ministry of foreign affairs, talks.... on agreements and arrangements for long-term co-operation and friendship, including agreement on temporary US troop presence in Iraq," the Iraqi foreign ministry said.
US troops in Iraq currently operate under a United Nations mandate, but this expires at the end of the year, and the two sides are negotiating guidelines which would allow them to remain.
Iraq has said it does not want the UN mandate renewed, and correspondents say the shape and size of a longer-term US presence will be a key issue.