BAGHDAD, Iraq (CNN) -- Violence gripped northern Iraq on Tuesday as a suicide bomber killed at least one person in Mosul and authorities found nine bodies and an additional 10 decapitated heads in Diyala province.
Tuesday's incidents followed a roadside bombing in Mosul the previous day that killed five U.S. soldiers, a massive explosion in that city last week that killed 60 people and the slaying of a provincial police chief as he inspected the explosion site.
But attacks were not limited to the north Tuesday, with at least 14 people wounded in roadside bombings in Baghdad, according to police.
The U.S. military recently described Mosul as the only major Iraqi city with a considerable presence of al Qaeda in Iraq fighters.
Diyala province, where the bodies and heads were found, has long been a volatile region, and the U.S. military has spearheaded operations there against militants during the past year's so-called troop surge.
Ahmed Fuad, morgue director in Diyala's capital, Baquba, said police found the remains near Muqtadya and they will be handed over to families if they bring a letter from police allowing their release.
Authorities said they think some victims may have been part of al Qaeda in Iraq.
Tuesday's suicide bombing in Mosul targeted a U.S. military convoy, according to police. There were no American casualties, the military said, but 15 Iraqis were injured in addition to the person killed in the strike.
This month, the U.S. military launched Operation Iron Harvest, an offensive to root out insurgents in four northern provinces: Nineveh, where Mosul is located, and Diyala, Tameem and Salaheddin. Iraqi forces also are taking part in the operation.
Iraqi authorities in recent days announced a major deployment of Iraqi troops to Mosul as a prelude to a planned offensive intended to clear the area of al Qaeda in Iraq militants.
So far in January, 36 U.S. troops have died in Iraq, with 23 killed in the north -- a toll that reflects the military focus on that region. There have been 3,940 American military deaths in the nearly 5-year-old Iraq war, including seven civilian employees of the Defense Department.
Tuesday's roadside bombings in Baghdad targeted security forces, police said. Three soldiers, three police officers and eight civilians were injured.
U.S.-led coalition troops on Tuesday seized 18 people described as "suspected terrorists" during raids against al Qaeda in Iraq and other militants, the U.S. military said.
"Each capture is another step forward on the path to an Iraq free from al Qaeda's violence," said Maj. Winfield Danielson in a reference to al Qaeda in Iraq. "While al Qaeda is still capable of brutal and spectacular attacks, we are working to dismantle their networks and keep them off balance."
In Washington, the Army said it has opened a criminal investigation into allegations that members of the 1st Infantry Division killed Iraqis captured in the field last spring and summer.
The Army announced the probe in a news release posted late Friday on its Web site.
A soldier recently came forward with information pertaining to allegations, two Army officials said. Initial information indicates up to six Iraqis may have died.
The "preliminary findings indicate the deceased detainees were not persons detained in a detention facility," the Army news release said.
The allegations involve members of the 1st Infantry Division's 2nd Brigade Combat Team.
It was deployed to Iraq from September 2006 through November in southwest Baghdad's Rashid district. The unit has returned to its home base in Schweinfurt, Germany. E-mail to a friend
CNN's Jomana Karadsheh, Erin McLaughlin and Ahmed Taha contributed to this report.