Violence in Baghdad and north Iraq killed 17 people on Friday as throngs of Shiite pilgrims converged on the Iraqi capital for annual commemoration rituals amid heavy security.
The unrest comes as Iraq grapples with a protracted surge in bloodshed that has left more than 3,700 people dead so far this year and fulled fears the country is slipping back into all-out conflict.
Friday's deadly violence struck in the capital and the restive northern province of Nineveh, leaving 17 people dead and 25 others wounded, security and medical officials said.
Mortar fire in north Baghdad killed three people, while two men were shot dead in the west of the capital.
The mortar rounds slammed into the Zahra neighbourhood adjacent to Kadhimiyah, where tens of thousands of Shiite Muslims prepare to commemorate the death of a revered figure in Shiite Islam.
For days worshippers from across the country have been walking to Kadhimiyah, site of a shrine dedicated to Imam Musa Kadhim, the seventh of 12 revered imams in Shiite Islam, who died in 799 AD.
The commemoration rituals climax on Saturday and Sunday.
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Shiite pilgrims are often targeted by Sunni militants who regard them as apostates. In past years, multiple attacks have been carried out during the Imam Kadhim commemorations.
Due to the heightened threat of attack, the authorities have imposed heavy security measures on the capital, involving the closure of entire roads and barring certain vehicles from the streets.
In Nineveh province, north of the capital, four more people were killed on Friday, including two senior police officers, officials said, while attacks elsewhere north of Baghdad killed eight others.
Violence has surged in the past year to its highest level since 2008, while anti-government fighters control an entire city a short drive from Baghdad and parts of another.
The latest attacks come as Iraq's political parties jostle to build alliances and form a government after April polls that left incumbent Prime Minister Nuri al-Maliki in the driver's seat to remain in office for a third term.
The authorities have trumpeted security operations against militants, saying on Friday that they killed 35 more insurgents, and blame external factors such as the civil war in neighbouring Syria for the surge in violence.
Analysts and diplomats, however, say the Shiite-led government must do more to reach out to disgruntled minority Sunnis and undermine support for militancy.