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.
Today'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.
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 tomorrow and on Sunday.
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.
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.
