Kabul, Afghanistan ? U.S. military officials said Wednesday they feared all 17 troops aboard a special operations helicopter were dead after hostile fire downed the craft and it slid or rolled into a rugged mountain ravine in eastern Afghanistan.

If those aboard were confirmed killed, the crash would be the deadliest blow yet to American forces in Afghanistan, already grappling with an insurgency that is widening rather than winding down.

The officials said they knew of no communications from the crash site, accessible only by foot.

Stormy weather hampered rescue efforts after the MH-47 helicopter crashed Tuesday while ferrying in reinforcements for troops already on the ground pursuing al-Qaida militants near the border with Pakistan.

The officials cited reports from the region that the helicopter struck or landed badly on the side of a mountain then went down into the ravine, suggesting little hope of survival. They said, however, they could not confirm the deaths, and spoke on condition of anonymity since rescue operations were still under way.

Only eight months ago, Afghan and U.S. officials were hailing a relatively peaceful presidential election here as a sign that the Taliban rebellion was finished. That bravado has been yet another casualty in a war some feel could escalate into a conflict on the scale of Iraq’s.

The loss of the helicopter follows three months of unprecedented fighting that has killed about 465 suspected insurgents, 43 Afghan police and soldiers, 125 civilians, and 29 U.S. troops. Afghan and U.S. officials have predicted the situation will deteriorate before legislative elections are held in September.

The Taliban have stepped up attacks, and there are disturbing signs that foreign fighters – including al-Qaida – might be making a new push to sow mayhem. Afghan officials say the fighters have used the porous border with Pakistan to enter the country, and have called on the Pakistani government do more to stop them.

Even before the crash was announced, a Taliban spokesman claimed responsibility and said he had footage of the attack. As of Wednesday, no video had surfaced.

U.S. military spokesman Col. James Yonts said the helicopter was fired on as it was approaching a landing zone while rushing reinforcements to a battle in an area known to harbor “terrorist organizations.” It flew on, but crashed about a little over a mile away at dusk, he said.

“The aircraft was taking indirect fire and direct fire from elements on the ground,” he said.

Coalition and Afghan troops “quickly moved into position around the crash to block any enemy movement toward or away from the site,” a U.S. military statement said. Yonts said fighting was continuing Wednesday.