KABUL, Afghanistan — Five Americans and two other soldiers, a Briton and Canadian, died when a Chinook helicopter was apparently shot down Wednesday in Afghanistan's most volatile province, a U.S. military official said. The Taliban claimed responsibility.

NATO's International Security Assistance Force said other troops rushing to the scene were ambushed and had to call in air support to drive off their attackers.

Initial reports suggested the helicopter was hit with a rocket-propelled grenade, said the U.S. official, who insisted on speaking anonymously because the crash was still under investigation. NATO said there were no survivors.

A purported Taliban spokesman, Qari Yousef Ahmadi, claimed in a phone call to The Associated Press that militants shot the helicopter down in southern Helmand province, the world's largest opium poppy-growing region where combat has been heavy in recent months.

Meanwhile, the Pentagon said Wednesday that a U.S. helicopter that crashed and killed two soldiers in Iraq's Diyala province Monday was shot down by enemy fire.

Brig. Gen. Perry Wiggins, deputy director of operations for the Joint Chiefs of Staff, said the military believes the aircraft was brought down by small arms fire, and that the roadside bomb that killed a response team headed to the crash site was not the newer, armor piercing explosively formed penetrators, or EFPs, that have killed hundreds of U.S. soldiers.

Other developments in Iraq:

• American and Iraqi troops raided Baghdad's Sadr City neighborhood on Wednesday, looking for five British citizens abducted a day earlier from a nearby government building, military and diplomatic officials said.

• The United States has finalized new guidelines that will soon begin admitting a bigger trickle of the more than 2 million refugees who have fled Iraq, acknowledging for the first time the country may never be safe for some who have helped the United States.