BAGHDAD, Iraq (CNN) -- Conflict flared up Wednesday in an area of northern Iraq where U.S. and Iraqi troops have been taking on al Qaeda in Iraq and other militants.
A U.S. soldier mans a watchtower Wednesday near Baghdad, Iraq.
A powerful blast leveled an apartment building, a suicide car bomb exploded in a crowded marketplace, and the U.S. military reported a series of raids on insurgent targets.
Officials said at least 17 people were killed in blasts Wednesday across the region, and the U.S. military said American-led coalition raids killed at least 20 militants Tuesday and Wednesday.
An explosion ripped through an apartment building, killing 12 people and wounding more than 130, in Zanjili, south of Mosul in Nineveh province, the U.S. military said.
Mosul police said the explosion happened as the Iraqi army was headed to the building after receiving a tip about a weapons cache there. Authorities suspect the cache somehow detonated, causing the structure to collapse and destroying nearby houses.
Police said at least five people were killed and 11 wounded when a suicide car bomb exploded in the Debis district near the northern city of Kirkuk in Tameem province.
The bomber was targeting a convoy of a Kirkuk Police Academy official in a crowded marketplace in a predominantly Kurdish area, authorities said. Police said they expect the toll to rise. Debis, about 21 miles north of Kirkuk, has not experienced a major attack since 2003.
The U.S. military said coalition forces in Iraq killed 15 "terrorists" on Tuesday and Wednesday in operations against al Qaeda in Iraq north of Baquba in Diyala province.
Troops targeted an al Qaeda in Iraq leader in a Diyala raid Tuesday, leading to a firefight, the military said. Two militants were killed in the gunbattle, including the militant leader.
Troops returned to the area Wednesday looking for an associate of the leader.
"As coalition forces arrived in the target area, they observed a group of enemy personnel moving into fighting positions. Responding in self-defense, the ground force called supporting aircraft to engage the hostile force, killing 10 terrorists," the military said in a news release.
Three more militants were killed as troops worked to clear the area, and they also found weapons caches.
The U.S. military also reported that coalition troops killed five militants Tuesday in an operation east of Samarra in Salaheddin province. The troops captured one person in Samarra overnight and 13 people in Mosul on Wednesday.
The U.S. and Iraqi militaries have been conducting an anti-insurgent offensive called Operation Iron Harvest in four northern provinces -- Diyala, Salaheddin, Nineveh and Tameem -- but the military said Wednesday's raids were not part of that operation. E-mail to a friend
CNN's Jomana Karadsheh contributed to this report.