URMUL, Afghanistan — The silence was deceptive as the American patrol edged along a deep, snow-bound valley in the remotest reaches of eastern Afghanistan.

Ignoring a winter lull in hostilities, the soldiers had set off to pursue a local commander allied to Taliban fighters. Radio intercepts showed that insurgents were tracking the men from Alpha Troop of the 3rd Squadron, 71st Cavalry. But this time, there was no ambush.

“We pushed the commander out of the village,” Alpha Troop’s commanding officer, Captain Matt Gooding, said. “I want to make sure he has an uncomfortable, cold night.”

Last summer, these soldiers arrived in the Afghan province of Nuristan, a morass of steep, wooded valleys in the Hindu Kush Mountains bordering Pakistan.

Their camp at the village of Urmul — possibly the American military’s most vulnerable outpost in Afghanistan — was attacked every day for the first 10 days of its existence.

Conventional forces from the American-led coalition had never previously entered Nuristan, nor had Afghanistan’s central government exerted any control over this distant province.

Instead, it had become a fiefdom of the veteran Taliban-allied warlord Gulbuddin Hekmatyar.

Intelligence reports say this area might also be a refuge for Osama bin Laden.

The possibility that the world’s most wanted man lurks in these mountains is never far from the minds of the American soldiers in Urmul.

“It is possible this is a haven for ‘the man,'” Captain Gooding said. “I could not believe they sent conventional forces into this terrain — this is more suited to special forces.”

His troops do not have the equipment or training of special forces, yet they are fighting in some of the world’s harshest terrain.

The danger that they face can be gauged by the fact that France is withdrawing all its special forces from Afghanistan after they suffered unacceptably high casualties.

The regular forces of the 71st Cavalry are left in their mountain outpost, wedged beneath 15,000-foot peaks at the confluence of two rivers.

The arrival of spring in six weeks heralds the renewal of the fighting season and the Taliban, encouraged by last year’s revival, have vowed to attack foreign forces with greater intensity.

Captain Gooding’s troops have penetrated the wilder reaches of eastern Afghanistan and laid the ground for further operations against Al Qaeda and Taliban fighters.

But the quest for Mr. bin Laden in Nuristan may already be futile.

Afghan intelligence arrested a Pakistani in neighboring Kunar province last month who, they claim, was an agent of Pakistan’s Interservice Intelligence agency.

Sayed Akbar is reported to have confessed during interrogation that he joined two other ISI officers to aid Mr. bin Laden’s passage from Nuristan across the border to Chitral in Pakistan in October 2005.

Lieutenant Colonel Michael Howard, who commands 3rd Squadron, said his sights were on less lofty targets like winning over local people who have hitherto backed Mr. Hekmatyar’s Hezbi-i-Islami group.

His unit performs a “blocking” role to interrupt insurgents filtering across the frontier to Kunar, which American soldiers describe as a “mini-Iraq.”

“We have seen them coming across the border on several occasions in groups of 20 to 30,” Colonel Howard said.

However, despite the reconnaissance scouts’ specialized “optics” that pinpoint enemy fighters, it is often difficult to find the enemy in a land steeped in intrigue. Before it converted to Islam in the 19th century, Nuristan was known as Kafiristan, “land of infidels.”

Kipling chose its then-unexplored mountains as the setting for his short story “The Man Who Would Be King.”

Until last month, every time Chinook helicopters reached the American camp by delicately navigating onto a tiny landing pad beside the river, they drew rocket fire. “Due to enemy fire, or bad weather, no ‘birds’ could land for a while. We had zero fuel,” Captain Gooding said.

“I couldn’t even roll a truck.”

Until a month ago, before heavy snow sealed the border passes, soldiers at the camp endured constant rocket-propelled grenade attacks launched from adjacent ridges. Insurgents stashed weapons in nearby caves, and almost every patrol on the area’s only road was ambushed.

The unit retaliated by calling in Apache helicopters and B1 strike aircraft with 2,000-pound bombs.

“They said that we would never be able to sustain an outpost here,” the camp’s civil affairs officer, Major Brian Troglia, said.

“But here we are.”