KABUL, Afghanistan - Ten U.S. soldiers died when their helicopter crashed during combat operations aimed at flushing out militants from remote mountains in eastern Afghanistan, officials said Saturday.

News of the crash came the same day a top U.S. official called parts of Pakistan's mountainous border region a "safe haven" for militants and said Osama bin Laden was more likely to be hiding there than in Afghanistan.

The crash of the CH-47 Chinook Friday afternoon was the deadliest for U.S. forces here in a year and comes at a time of increasing militant attacks, though U.S. officials ruled out hostile fire as a cause.

"There is no indication that the helicopter came down due to some enemy action," Lt. Tamara D. Lawrence, a coalition spokeswoman, told The Associated Press.

Some 2,500 Afghan and U.S. soldiers are conducting a joint military campaign, dubbed Operation Mountain Lion, in Kunar province near the border with Pakistan. It is one of the biggest offensives since the ouster of the hard-line Taliban regime by U.S.-led forces in late 2001 for hosting al-Qaida.

The transport helicopter was conducting "operations on a mountaintop landing zone" when it crashed near Asadabad in Kunar, about 150 miles east of the capital, Kabul, the military said.

The terrain surrounding Asadabad ¡ª where the U.S. military has a large base ¡ª is extremely rugged. The police chief of Kunar province, Gen. Abdul Ghafar, said the helicopter crashed about 10 miles northwest of the base at a remote spot a day's walk from any passable road.

"The area of the crash is a mountainous area and it is difficult to reach," Ghafar said.

Recovery operations did not begin until daybreak Saturday. The military did not say what unit the U.S. troops were from, only specifying that they were soldiers.

Attacks have been on the rise in Afghanistan's southern and eastern provinces, where militants have been using suicide and roadside bombs more than ever.

The 10 deaths brought to at least 25 the number of U.S. military personnel killed in Afghanistan this year, according to the Web site icasualties.org, which relies on Defense Department information.

At least 234 U.S. military personnel, including those killed Friday, have died in Afghanistan as well as neighboring Pakistan and Uzbekistan as a result of the conflict, according to the Defense Department.

Also Saturday, a top U.S. counterterrorism official said that bin Laden was more likely to be hiding in Pakistan than in Afghanistan.

Henry Crumpton, the U.S. ambassador in charge of counterterrorism, lauded Pakistan for arresting "hundreds and hundreds" of al-Qaida figures but said it needed to do more.

The chief spokesman for Pakistan's army, Maj. Gen. Shaukat Sultan, dismissed Crumpton's assertions as "absurd."

Pakistan has launched repeated counterterrorism operations in its lawless tribal regions over the past two years and hundreds of militants and soldiers have been killed.

"Our expectation is that they will continue to make progress, and we know that it's difficult," Crumpton said. Pakistan "can't remain a safe haven for enemy forces, and right now parts of Pakistan are indeed that."

A U.S. military statement said that other aircraft and crews were near the landing zone during Friday's crash.

A purported Taliban spokesman, Mohammed Hanif, called AP to claim that Taliban militants had shot down the helicopter using a "new weapon" that he refused to specify.

The phone call did not come until after news of the crash was made public, and Lawrence dismissed the claim.

"The Taliban have made those claims before and they have turned out to be completely false, and there's absolutely no indication that hostile action caused this crash," Lawrence said.

Last June, all 16 troops on board a Chinook died in Kunar when it was hit by a militant's rocket-propelled grenade ¡ª the deadliest attack against American forces in Afghanistan.

In September, a Chinook helicopter crashed in a mountainous area in southeastern province of Zabul, killing all five American crew members.