Insurgents unleashed a string of bomb attacks mainly targeting Shiite Muslim pilgrims across Iraq on Thursday, killing at least 22 people and extending a wave of deadly bloodshed into a second day.

The eruption of violence follows nearly two weeks of relative calm, and threatens to enflame rising tensions among Iraq's ethnic and sectarian groups.

The worst attack took place near Dujail, 80 kilometers (50 miles) north of Baghdad, where a pair of car bombs exploded near pilgrims who were traveling on foot to a shrine in the town of Samarra.

The head of the Salahuddin provincial health directorate, Raed Ibrahim, said 11 people were killed and more than 60 were wounded in that attack.

"We heard thunderous explosions, and everybody went outside and saw burning cars and several bodies on the ground. Market stalls on both sides of the road were on fire," said Naseer Hadi, who works in the Dujail post office.

The pilgrims were heading to Samarra to commemorate the death of two prominent Shiite Imams who are buried in the al-Askari shrine there.

A 2006 bombing at the gold-domed shrine that was blamed on al-Qaida in Iraq set off years of retaliatory bloodshed between Sunni and Shiite extremists that left thousands of Iraqis dead and pushed the country to the brink of civil war.

The attacks in Dujail came hours after a car bomb struck a bus carrying foreign pilgrims near the southern Shiite holy city of Karbala. Four people were killed and 12 were wounded in that attack, according to police and hospital officials.

The explosion tore through the undercarriage and blew out most of the windows of the white and blue tour bus that got hit. Nusaif al-Kitabi, deputy chairman of the Karbala provincial council, said the bus was carrying pilgrims from Afghanistan.

In the town of Qassim, 125 kilometers (78 miles) south of Baghdad, a parked car bomb exploded near a bus stop, killing five people and wounding 20. The casualties included Shiite pilgrims who were heading to Karbala, said police and hospital officials.

Shiite pilgrims are a favorite target for Sunni insurgents who seek to undermine the country's Shiite-led government and provoke a return to sectarian fighting.

In northeastern Baghdad, a roadside bomb apparently meant to hit an army patrol missed its target and struck a civilian car, killing 2 passengers and wounding two others, said police and hospital officials. Like most other officials, they spoke on condition of anonymity because they were not authorized to release the information to reporters.

Thursday's bloodshed comes a day after a wave of attacks killed at least 33 people across Iraq in the country's deadliest day in more than a month.

The worst of Wednesday's attacks struck in the northern city of Kirkuk, where a car bomb hit outside the offices of the Kurdistan Democratic Party, killing 19. The KDP is led by Massoud Barzani, the president of Iraq's largely autonomous Kurdish region, who has frequently sparred with the central government in Baghdad.

___

Associated Press writers Adam Schreck and Qassim Abdul-Zahra contributed to this report.