BAGHDAD: Insurgents unleashed a string of bomb attacks mainly targeting Shiite Muslim pilgrims across Iraq on Thursday, killing at least 26 people and extending a deadly wave of bloodshed into a second day.

The violence that left nearly 60 dead since Wednesday morning followed nearly two weeks of relative calm and threatened to fuel rising tensions among Iraq's ethnic and sectarian groups. Shiite pilgrims are a favorite target for Sunni insurgents who seek to undermine the country's Shiite-led government and provoke sectarian fighting.

The worst attack was near Dujail, 80 kilometers (50 miles) north of Baghdad, where a pair of car bombs exploded near pilgrims who were walking 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.

"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 there in the al-Askari shrine.

Associated Press video showed a damaged Shiite mosque and shattered shop windows.

A 2006 bombing at the gold-domed shrine that was blamed on al-Qaida in Iraq sparked years of retaliatory bloodshed between Sunni and Shiite extremists.

The violence 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 of the white and blue tour bus and blew out most of its windows. Nusaif al-Kitabi, deputy chairman of the Karbala provincial council, said the bus was carrying pilgrims from Afghanistan.

In the evening, a roadside bomb blew up as pilgrims walked to Karbala's Imam Hussein shrine, one of the holiest sites for Shiites, wounding two.

Seconds later, a car bomb exploded near a small restaurant in the city, killing two pilgrims and wounding 7 others, according to police and hospital officials.

In the town of Qassim, 125 kilometers (78 miles) south of Baghdad, a bomb placed in a parked car exploded near a bus stop, killing seven people and wounding 28. The casualties included Shiite pilgrims who were heading to Karbala, said police and hospital officials.

In northeastern Baghdad, a roadside bomb apparently targeting an army patrol struck a civilian car instead, killing two passengers and wounding two others, said police and hospital officials. The officials spoke on condition of anonymity because they were not authorized to release the information to reporters.

Thursday's bloodshed came 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 was in the northern city of Kirkuk where a car bomb exploded 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.

Late Thursday, Iraqi state TV announced that the country's border with Jordan would be reopened for the first time in more than a week.

Iraqi authorities citing unspecified security concerns shut the busy frontier crossing on Jan. 9, cutting a key route through a part of the country where anti-government protests fueled by perceived discrimination by Iraq's minority Sunni Arabs have been raging for weeks.