|The Shrine of Imam Hussein in the holy Shia city of Karbala is one of the sites frequented by pilgrims [Gallo/Getty]
Twin bombings targeting Iranian pilgrims have killed at least 13 people in Iraq's holy Shia cities of Karbala and Najaf.
In the first attack a bus carrying pilgrims was hit by a bomb explosion in Touirij town near Karbala in central Iraq, killing at least 10 people and injuring another 38 on Monday.
In the second incident, a car bomb exploded near buses transporting Iranian pilgrims in the city of Najaf, killing at least three people and wounding 10 others.
The revered Imam Ali shrine in Najaf attracts hundreds of thousands of Shia Muslims from Iraq, Iran and other countries every year.
According to officials, the first explosion occurred at a parking lot in the northern part of the Karbala.
"It was a suicide bomber who drove up against a bus carrying Iranian pilgrims and detonated the explosives," a police official told AFP news agency.
The explosion wounded another 38 people, most of them Iranians, hospital officials said.
Mohammed al-Moussawi, head of the Kerbala provincial council, said that the Iranian pilgrims were the targets of the attack.
Some 1,500 pilgrims from neighbouring Iran visit Shia shrines in Iraq a day, mainly in the holy cities of Najaf and Karbala.
Also on Monday, a car bomb exploded in the southern city of Basra killing at least 12 people and wounding 39 others.
The blast happened near a busy street filled with restaurants and shops in the city's Qibla district.
Political tensions in Iraq have been stoked by the failure of its leaders to agree on a new government eight months after an inconclusive election.
Nouri al-Maliki, the incumbent prime minister, a Shia, is close to securing a second term but is still trying to win over leaders of a Sunni-backed cross-sectarian alliance.
The attacks come ahead of the Islamic month of Muharram, in which Shia Muslims mourn the historic battle of Karbala.