Two bombs exploded near crowds of Shi'ite pilgrims walking through Iraq's capital Monday, killing at least 15 people and wounding 52 others, police and hospital sources said.

Thousands of Shi'ites are making the annual pilgrimage to the holy city of Kerbala for the Arbain religious rite amid Iraq's worst political crisis in a year after the Shi'ite-led government moved against two prominent Sunni politicians.

The crisis threatens to unravel Iraq's fragile coalition government of Shi'ite, Sunni and Kurdish factions and has raised fears of renewed sectarian violence.

Police and hospital sources said a suicide bomber drove a car from a side road into a group of pilgrims in a main road in the Bayaa district of southwestern Baghdad, killing nine people and wounding 28 others.

In the northern Shaab district of the capital, a car parked near a market exploded, killing two civilians and four police officers assigned to protect the pilgrims, and wounding 24 other people, the sources said.

The explosion had little impact on the market because it was tucked behind thick concrete blast walls. Unprotected pilgrims on the other side of the road got the brunt of the explosion, a police officer said.

Shi'ite pilgrims have been under attack for days in Iraq.

The explosion of two roadside bombs in southern Baghdad earlier in the day killed at least two people and wounded 12, while a sticky bomb attached to a bus carrying Afghan pilgrims blew up late Sunday, wounding nine.

Last Thursday, bombings in mainly Shi'ite areas killed at least 73 people and wounded scores of others. The largest toll occurred at a police checkpoint near the southern city of Nassiriya where a suicide bomber killed 44 and wounded 81.

Arbain marks the end of a 40-day mourning period for Imam Hussein, a grandson of the Prophet Mohammed who was killed in a 7th century battle in Kerbala. Shi'ites believe his remains are entombed there.

Shi'ite rituals have been a target for attacks since Saddam Hussein was ousted in the U.S.-led invasion of 2003. Some Sunni Islamist groups such as al Qaeda view Shi'ites as heretics.

The annual event draws hundreds of thousands from Iraq's Shi'ite majority who were unable to practise such rites freely under Saddam, a Sunni Arab. Thousands of Shi'ites come to Iraq from other countries, mainly neighboring Iran, for the rite.

Iraq's worst political crisis since the contentious formation of its cross-sectarian government in 2010 erupted when Shi'ite Prime Minister Nuri al-Maliki sought the arrest of Sunni Vice President Tareq al-Hashemi and the removal of Maliki's Sunni deputy, Saleh al-Mutlaq.

The moves came shortly after the last U.S. troops left Iraq on December 18 and were followed a few days later by a series of bombings in mainly Shi'ite areas of Baghdad that killed more than 70 people, reviving concerns of renewed sectarian conflict.

Thousands of people were killed by the sectarian slaughter unleashed by the 2003 invasion that toppled Saddam.

(Writing by Jim Loney; Editing by Matthew Jones)