MOSUL, Iraq - U.S. troops hauled away the wreckage of two Black Hawk helicopters yesterday to begin an investigation into a deadly collision over this city in northern Iraq as another audiotape purportedly from ousted Iraqi leader Saddam Hussein warned of more attacks on U.S. soldiers.

The helicopter crash killed 17 American soldiers and injured five others, the deadliest single incident for U.S. troops since the war began in March. As troops used cranes and flatbed trucks to cart away the wreckage, Army officials said they had no quick answer on the cause of the midair collision.

As investigators worked to determine whether insurgents played a role in the crash, an Arabic television station aired an audiotape last night, said to be from Hussein, calling on Iraqis to wage holy war against the occupying force.

"Fighting them is a legitimate, patriotic and humanitarian duty, and the occupiers have no choice but to leave our country, Iraq, the country of Arabs and Islam, as cursed losers," the speaker said. He added that "the path of jihad and resistance is the best path" to expel "tyrannical foreign forces from our country and grant total freedom and sovereignty to our people."

The tape, dated this month and broadcast by the Dubai-based satellite channel Al-Arabiya, apparently was released to mark the Muslim holy month of Ramadan.

Meanwhile, U.S. forces continued their new strategy of using heavier firepower on suspected guerrilla bases and conducting aggressive roundups of weapons in Baghdad and other cities.

Troops backed by armored vehicles and helicopters sealed off a 20-block area in the capital while they searched cars and trucks, and explosions were heard later in the evening in Baghdad that military officials suggested were bombings of suspected rebel hide-outs.

A spokesman for the 4th Infantry Division said soldiers fired a satellite-guided missile containing a 500-pound warhead at a suspected guerrilla training base near Kirkuk yesterday. Four insurgents were killed in a separate clash.

In Tikrit, Army units fired artillery and tank rounds at rebel positions early this morning, destroying a number of houses.

"Any of those groups that are working against the best interest of the Iraqis are going to be targeted," said Lt. Col. William MacDonald, a spokesman for the 4th Infantry Division.

President Bush, talking to reporters upon his return to the White House from Camp David, addressed the new Hussein tape and criticism that the administration was embarking on a cut-and-run strategy in Iraq.

"I suspect it's all the same old stuff," he said, referring to the Hussein tape. "It's propaganda."

Asked about Iraq, he added: "We're not leaving till the job is done, plain and simple."

Meanwhile, U.S. officers involved in the hunt for weapons of mass destruction said the Iraqi scientist who led Hussein's long-range missile program has fled to neighboring Iran, the Associated Press reported.

Dr. Modher Sadeq-Saba al-Tamimi's departure comes as top weapons makers from Hussein's deposed regime find themselves out of work but with skills that could be useful to militaries or terrorist organizations in neighboring countries. U.S. officials say some of them are now in Syria and Jordan.

"There are a couple hundred Iraqis who are really good scientists, particularly in the missile area," said Jonathan Tucker, a former United Nations inspector now with the Center for Nonproliferation Studies at the Monterey Institute in California. "In the chemical and biological areas, their work wasn't state of the art, but it was good enough to be of interest to other countries."

Also yesterday, the Department of Defense said all of the dead in Saturday's helicopter crash were from the 101st Airborne Division, based in Fort Campbell, Ky.

Only five were identified yesterday: Army Spc. William D. Dusenbery, 30, of Fairview Heights, Ill.; Sgt. Michael D. Acklin II, 25, of Louisville, Ky.; Spc. Ryan T. Baker, 24, of Brown Mills, N.J.; Sgt. Warren S. Hansen, 36, of Clintonville, Wis.; and Spc. Eugene A. Uhl III, 21, of Amherst, Wis.

The Chicago Tribune is a Tribune Publishing newspaper. Wire services contributed to this article.