BAGHDAD — A suicide truck bomber who concealed his explosives under tanned animal hides struck a U.S. patrol base Sunday in northern Iraq, killing one U.S. soldier and wounding 18 other Americans, U.S. and Iraqi officials said.

Two Iraqi contractors working at the base in Tamim province also were wounded, according to a brief statement from the military.

Tamim has a mixed population of Arabs, Kurds and Turkomen, with the oil-rich city of Kirkuk as its capital. Three American soldiers were killed last Wednesday by gunfire in Tamim.

Brig. Sarhat Qadir, a senior officer in the Kirkuk police department, said the bomber targeted a U.S. patrol base in a mostly Sunni Arab residential area in Rashad, about 25 miles southwest of Kirkuk.

The suicide attacker rammed his vehicle into blast walls outside the gates of the small U.S. base, located in a residential neighborhood of Sunni Arabs, Qadir said. He added that the explosives were concealed under tanned animal hides.

Earlier, the U.S. military issued a statement saying an American soldier died late Saturday when his vehicle was struck by a roadside bomb in eastern Baghdad.

At least 4,094 members of the U.S. military have died in the Iraq war since it began in March 2003, according to an Associated Press count.

In Baghdad, four police recruits were killed in a blast at the National Police headquarters, authorities said.

Another 22 people were wounded near the building's gate where recruits were gathering, they said. Police gave conflicting reports about whether the attack used mortars or a roadside bomb.

A mortar shell landed just outside Baghdad's Green Zone on Sunday, killing three civilians and wounding seven others, police said.

The mortar was apparently targeting the Defense Ministry, which is inside the U.S.-guarded diplomatic zone, but fell short, they said.