A female suicide bomber has blown herself up among Shia pilgrims near Baghdad, killing at least 41 people and wounding 106.
The bombing took place as thousands of Shia Muslims arrived for the start of a trek to the southern city of Kerbala for the religious rite of Arbain.
An Interior Ministry source and a police official said the attack took place on a tent where pilgrims are given food and drink.
The bombing occurred as the country prepares for a March election when Prime Minister Nuri al-Maliki's government is expected to campaign on improved security.
More attacks are likely during the Arbain religious period and before the election as suspected Sunni Islamist groups try to undermine Mr Maliki's Shia-led government.
Millions of Shias from Iraq, Iran, Bahrain and other nations have defied the threat of suicide bombings to visit Iraq's Shia holy sites.
Arbain marks 40 days of mourning for Hussein, the Prophet Mohammad's grandson, who died in a seventh century battle at Kerbala.
Hundreds of thousands of pilgrims, beating their heads and chests in ritual mourning, pour into the city for the rite.
Tens of thousands of troops and police have been deployed to protect pilgrims and also around the revered Imam Hussein shrine in Kerbala.
