BAGHDAD — A roadside bomb killed three American soldiers and an interpreter north of Baghdad, the U.S. military said today, and Iraqi police reported 14 Shiite gunmen were arrested after fighting south of the capital.

In Baghdad, meanwhile, American soldiers using specially trained dogs sifted through the wreckage today of an office in Sadr City where a bomb killed 10 people, including four Americans working to restore local government in the former Shiite militia stronghold.

The Iraqi Defense Ministry spokesman suggested that Iraqi officials — and not the Americans — were the main target.

Also today, U.S. soldiers in Baghdad killed three gunmen who fired on an American convoy that had stopped along the side of the road just west of the city's airport, the U.S. said. No further details were released.

The roadside bombing occurred about 10:45 p.m. Tuesday in Nineveh province, where al-Qaida in Iraq and other Sunni extremist groups remain active. The U.S. statement contained no further details.

The fighting in the south broke out before dawn near Nassiriyah, 200 miles south of Baghdad, as Iraqi forces were conducting house-to-house searches for Shiite militants.

Nassiriyah police chief Brig. Gen. Sabah al-Fatlawi said 14 suspects had been arrested but that sporadic clashes were continuing. The area is a stronghold of the Mahdi Army of anti-U.S. cleric Muqtada al-Sadr and has been plagued by power struggles between rival Shiite factions — some with close ties to the Shiite-led national government.