The U.S. military in Iraq says it believes one of Saddam Hussein's closest aides is directly involved in some of the attacks perpetrated against coalition forces. The coalition's new military spokesman, Brigadier General Mark Kimmitt, said U.S. forces have intensified their search for Saddam Hussein's deputy Izzat Ibrahim al-Douri.

The former leader of Saddam's Revolutionary Command Council is number six on the U.S. list of the 55 most-wanted Iraqis. "We're getting more intelligence that suggests he was directly implicated in the killing of some coalition soldiers. Are we any closer [to capturing him]? We're getting closer every day," said General Kimmitt.

General Kimmitt says the U.S. military is continuing a series of offensive operations it began last week in and around Saddam's hometown of Tikrit.

During a pre-dawn attack Monday, American troops fired tanks and mortars at positions which commanders said were being used by insurgents to attack soldiers. General Kimmitt says six insurgents were killed in the assault.

He also says U.S. soldiers in the city of Ramadi, west of Baghdad, have also arrested Kazim Mohammed Faris, a suspected organizer of Saddam Fedayeen fighters responsible for anti-coalition violence.

The U.S. military says it has adopted the new aggressive policy to match what it calls "clear changes in the enemy's tactics." More than 80 coalition troops have been killed this month in Iraq, including 17 soldiers who died Saturday when two U.S. Army Blackhawk helicopters collided and crashed in the northern city of Mosul.

There is still no official word on what caused the crashes. But eyewitnesses say one of helicopters may have been hit by a rocket-propelled grenade.

Meanwhile, violence claimed the lives of two more American soldiers Monday, north of Baghdad. One soldier was killed and two wounded in a rocket-propelled grenade attack. A few minutes later, another soldier was killed by a homemade bomb in the same area.

On Sunday, an audio tape, claiming to be the voice of Saddam Hussein, was broadcast on the Dubai-based Al-Arabiya television station. The speaker urged Iraqis to wage a holy war against coalition forces.

The Central Intelligence Agency says it is not clear whether the tape is genuine.