A bomb hidden under a parked car exploded near Muslim pilgrims Friday, killing at least two and wounding four as they made their way to an annual Shiite religious festival in a holy city south of Iraq's capital.

Pilgrims are an easy target for insurgents looking to stoke sectarian violence as U.S. troops prepare to depart Iraq by the end of the year.

Friday's bomb exploded in a parking lot about 14 miles (22 kilometers) from the holy city of Karbala, where thousands of pilgrims are flocking this weekend for the annual Shiite festival of Shabaniyah.

The blast ignited five nearby cars, causing a second explosion when a gas tank caught fire, said Maj. Gen. Othman al-Ghanimy, commander of Karbala military operations. Two pilgrims were killed and four wounded, he said.

Karbala provincial councilman Hussein Shadhan al-Aboudi put the toll at three dead and 28 injured.

The weekend's religious festival celebrates the birth of Mohammed al-Mahdi, the twelfth and so-called hidden imam, who disappeared in the ninth century. It is always held in the Islamic month before the Muslim fasting month Ramadan which this year falls in August.

Also Friday, a roadside bomb targeted a police patrol in Baghdad's southern Dora neighborhood, killing one passer-by and wounding three.

With Iraq still plagued by widespread violence, Washington and Baghdad are considering keeping as many as 10,000 U.S. forces in Iraq beyond a year-end departure deadline. In excepts from an interview to air Friday night, Prime Minister Nouri al-Maliki repeated his long-standing offer for a small number of American military trainers to stay and help Iraq's fledgling security forces.

Both nations are moving toward a troops withdrawal.

On Friday, officials said the last 10 Iraqi detainees in U.S. military custody are about to be turned over to Iraqi authorities.

Justice Ministry spokesman Haider al-Saadi said nearly 200 inmates were transferred to Iraq's custody earlier this week. They were among the last inmates to be held by the U.S. and included some top allies and relatives of former dictator Saddam Hussein.

The handover of the prisoners is the final step by the U.S. to relinquish control of Camp Cropper on Baghdad's western outskirts.

The process began a year ago, but since has been marred by high-profile escapes by some of its inmates.

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Associated Press Writers Saad Abdul-Kadir and Bushra Juhi contributed to this report.