PUL-E-ALAM, Afghanistan — Taliban fighters with assault rifles shredded an American aid group’s SUV with dozens of bullets yesterday, killing three Western women and their Afghan driver amid an escalating militant onslaught against humanitarian workers in Afghanistan.

The ambush of two clearly marked aid vehicles on the main road south of Kabul was the latest in a record number of attacks on aid groups this year — a surge that has workers questioning if they can safely provide services in remote and dangerous areas where help is most needed.

The group whose workers were slain, the New York-based International Rescue Committee, announced it was suspending its Afghan humanitarian programs indefinitely.

The Taliban claimed responsibility for the killings, saying its fighters attacked two vehicles of “the foreign invader forces.”

“They were not working for the interests of Afghanistan and they belonged to those countries whose forces … took Afghanistan’s freedom,” a Taliban spokesman, Zabiullah Mujahid, told the Associated Press in a phone call from an undisclosed location.

Mr. Mujahid called the women spies, a frequent Taliban accusation against its targets.

The aid group identified the women killed in Logar province as Nicole Dial, 30, a dual Trinidadian-American citizen; Jacqueline (Jackie) Kirk, 40, of Outrement, Quebec; and Shirley Case, 30, of Williams Lake, British Columbia.