Two American soldiers were killed Monday in separate incidents north of Baghdad, the U.S. military announced, while at least six Iraqi National Guardsmen died as the result of two car bomb attacks.

The U.S. military also announced Monday that it had charged two soldiers with premeditated murder in the death of an Iraqi civilian. The soldiers are attached to the same Army unit -- Company C, 1st Battalion, 41st Infantry Regiment, 1st Armored Division -- as two soldiers charged last week in the deaths of three Iraqis.

In none of the cases has the military provided any details of the allegations, except to say that the two sets of charges are unrelated.

Last week, the military concluded an unannounced court martial of a U.S. soldier for the murder of an Iraqi National Guardsman in May. Spec. Federico Merida was sentenced to 25 years in prison.

The two soldiers killed Monday were attached to the 1st Infantry Division. A statement from the military said both were killed in the town of Balad, about 40 miles north of Baghdad.

One soldier was killed when a U.S. patrol came under small-arms fire Monday morning. The patrol returned fire, the statement said. The second died in the same area when a U.S. military patrol vehicle swerved to avoid an Iraqi truck that was being driven erratically.

The first car bomb attack occurred in Mosul, a city north of Baghdad. At least three guardsmen were killed and three others wounded.

Later in the day in Fallujah, a stronghold of the Sunni Muslims that backed the rule of former president Saddam Hussein, a vehicle blew up near a security checkpoint, killing three guardsmen and injuring several others, the Associated Press reported.

Dozens of similar assaults have killed 90 Iraqi security forces or recruits during the past two weeks.

The nascent Iraqi security forces are the key to U.S. plans for bringing the insurgency under control and ultimately drawing down American troops. As Iraqi forces hit the streets over the next several months, U.S. commanders say, they will help provide the necessary stability for Iraq to hold nationwide elections before the end of January.

But the recruits have become the primary targets for insurgents seeking to undermine that strategy. In Baghdad, U.S. and Iraqi authorities say they believe the insurgents send suicide bombers to patrol the streets in search of large congregations of recruits.

In other developments Monday, U.S. forces continued attacks on insurgent targets in the Baghdad slum of Sadr City, the stronghold of rebel Shiite cleric Moqtada Sadr.

And news services reported that an Iranian diplomat taken hostage in Iraq last month was released by his captors. Fereidoun Jahani was seized as he traveled by car south of Baghdad by a group calling itself the Islamic Army in Iraq. It was not clear if he was being held by the same group when he was freed. Iran's state television said the kidnappers were from an unknown faction.

After his release, Jahani was taken to the Iranian embassy in Baghdad and was said to be in good health but tired.

There was no word on any of the other hostages being held in Iraq.