BAGHDAD: A car bomb killed at least eight people on a route taken by pilgrims returning from commemorations for a revered Shia imam in north Baghdad on Saturday, marring a ritual attended by tens of thousands.

An interior ministry official said the bomb, which exploded on the highway near Shuala in the north of the capital at about 12:15 pm killed eight people and wounded 18.

A medical source said that the Kadhimiyah and Al-Hakim hospitals between them had received 21 wounded people and the bodies of nine others.

The attack came as tens of thousands of Shia pilgrims flocked to the Kadhimiyah area for the climax of commemorations marking the death in 799 of Imam Musa Kadhim, the seventh of 12 revered imams, who is said to have been poisoned.

On Wednesday, 72 people were killed and more than 250 wounded in bomb and gun attacks across the country, with al Qaeda's local affiliate, the Islamic State of Iraq, claiming responsibility.

Those attacks included a car bomb on the outskirts of Kadhimiyah that killed seven people, and another blast in Karrada in central Baghdad amid pilgrims' food tents that caused 16 fatalities.

Saturday's ceremonies began about 8:00 am at the shrine.

“More people are attending the commemoration this year than in previous years,” said Karim Mohammed, 52.

“When we... see that there are explosions, it becomes a challenge to us, so those who decided not to go will go.”

Mohammed, who said he had walked for three days from Samarra, 110 kilometres north of Baghdad, had smeared mud on his face and is black robe in a sign of mourning.

“The imam is the symbol of martyrdom for Muslims in general, and especially for Shias,” said Abdullah Kitawi, 42, who said he walked for four days from Kut, 160 kilometres southeast of the city.

“Our mission is to preserve this commemoration as long as we live.”

Security measures in Kadhimiyah were tight, with anti-terrorism special forces deployed. Pilgrims were searched at various points, as helicopters clattered overhead.