A homicide bomber stalked members of a police intelligence unit, waiting for their night shifts to end, then attacked them outside a Baghdad restaurant Wednesday, killing three.

The blast was one of a spate of attacks around Iraq — including a homicide car bombing at a police checkpoint in the northern city of Mosul and the ambush-slaying of a Sunni sheik and his family north of Baghdad.

Violence in Iraq has dropped dramatically over the past 18 months, and was among the reasons President Barack Obama cited for his decision to end the U.S. combat mission here in August 2010. But there are growing concerns about a possible upward trend in violence after a series of deadly attacks in recent weeks on U.S. and Iraqi troops.

The Baghdad attacker struck the police employees as they stood near a restaurant in the Karradah neighborhood shortly after leaving work, said an aide to Maj. Gen. Qassim al-Mousawi, the Iraqi military spokesman. The aide said three were killed and four were wounded.

Police and hospital officials confirmed the death count but said 11 were wounded, including three civilians. All officials spoke on condition of anonymity because they were not authorized to release information.

A taxi driver, Salam Ali, said the security officials often eat breakfast at the restaurant after their night shifts are over.

Ali, 40, described burned and battered bodies scattered near the restaurant.

"I saw human flesh on the ground mixed with blood. It was an awful scene," he said.

Witnesses and officials described an equally gruesome scene in the northern city of Mosul. A suicide car bomb exploded at a crowded police checkpoint, killing at least two policemen and wounding 15 others, including eight policemen, according to an Iraqi police official.

The official said the bomber tried to reach the checkpoint by driving around a line of cars waiting to be searched. When policemen started to approach his vehicle, he detonated his explosives, the official said.

Hours later, gunmen killed an Iraqi soldier as he stood guard at a checkpoint in Mosul, a police official said.

The violence came as Iraqi security forces press ahead in the Mosul area with an offensive — dubbed "Operation New Hope" — that was launched last month against Al Qaeda in Iraq and other insurgents. U.S. and Iraqi officials have described Mosul, 225 miles northwest of Baghdad, as one of the insurgents' last urban strongholds.

Elsewhere on Wednesday, gunmen killed a Sunni sheik, his wife and two sons near Samarra, 60 miles north of Baghdad. The sheik and one of the sons were leaders in the Awakening Council movement opposed to Al Qaeda, a police official said.

The officials in both cities spoke on condition of anonymity because they were not authorized to release the information.

Meanwhile, the body of the son of a newspaper editor was found in Kirkuk, 180 miles north of Baghdad, police Brig. Sarhat Gadir said.

The son, identified as Munther Mohammed Shaheen, was found Tuesday more than a week after being kidnapped along with three others from a construction company in Kirkuk, Gadir said.

Shaheen's father is the editor of the now-closed al-Faisal newspaper, which began publishing after the 2003 invasion with assistance from U.S. authorities, Gadir said.

Also Wednesday, the U.S. military freed 20 prisoners a day after saying the number of their detainees has dropped to 13,832 from a peak of 26,000 in 2007.

U.S. forces have been releasing an average of 50 detainees a day, according to the military. The prisoners are being released or transferred to Iraqi custody to meet the requirements of a security agreement that took effect on Jan. 1.

Meanwhile, one of Iran's most powerful political and religious figures, former Iranian President Hashemi Rafsanjani, made a trip to the Shiite holy city of Karbala, 50 miles south of Baghdad.

Rafsanjani arrived in Iraq on Monday for talks with government and religious officials. Karbala is home to a shrine to Hussein, one of Shiite Islam's most revered saints.