Iraqi police say bombs have exploded on two buses near the southern city of Kut, killing at least 11 people and wounding 10 others.
The blasts near the mainly Shi'ite city follow a surge in violence last week, when truck bomb and mortar attacks killed about 100 people in Baghdad.
The attacks have brought new scrutiny to the Iraqi government's ability to ensure security. There are also indications of new political tensions within the Shi'ite majority government.
On Monday, major Shi'ite groups formed a new alliance that excludes Iraqi Prime Minister Nouri al-Maliki and his Dawa party.
Lawmakers said the new alliance will likely be led by the Supreme Islamic Iraqi Council, one of Iraq's most powerful Shi'ite groups. They said the alliance also includes followers of anti-U.S. cleric Moqtada al-Sadr, along with other influential groups and individuals.
The new coalition will replace the United Iraqi Alliance that was created for the 2005 election and included major Shi'ite parties.
The new alliance did not give a reason for excluding Dawa, but the party had been demanding a greater say in the grouping.
The announcement is the latest blow to Mr. Maliki, whose plan to remove the concrete barriers in Baghdad was reversed after last week's attacks. Mr. Maliki had said he hoped to remove the barriers as part of a return to normal life after years of violence.
But workers in Baghdad have begun placing a new line of protective concrete blast walls around the Foreign Ministry and other government buildings following last week's attacks.
Some information for this report was provided by AFP and Reuters.