WHEN the paratroopers of Chosen Company learnt that their battalion was to be sent to the mountains of southern Afghanistan instead of back to the deserts of Iraq, they heaved a collective sigh of relief.

“I thought it’d be pretty relaxed, that I’d be spending a lot of time in the gym,” Sergeant Timothy Smith recalled wryly. “I figured it was more of a peacekeeping mission than anything.”

But less than a month after setting up camp amid the rugged mountains of Zabul province, the heartland of the Taleban, they walked right into the battle of their lives — an intense hand-to-hand fight with what proved to be a surprisingly tenacious and determined enemy.

Dug into bunkers in an orchard in the remote village of Gazek Kula, armed with machineguns and rocketpropelled grenade launchers, dozens of Taleban fighters fought for hours with the Americans, about 50 of them to the death.

Weeks later the Americans were in action again, battling for almost 12 hours to oust at least 200 Taleban from the district headquarters in Miana Shin.

“It’s the most intense combat I’ve ever seen,” Sergeant Smith said. “They fight harder than anyone in Iraq ever did. I really never expected anything like this. We all kind of thought the Taleban were gone.”

They were not the only ones. After the Taleban failed to mount the promised campaign of disruption during last year’s presidential election, American military commanders and their Afghan counterparts confidently predicted that the rebel movement was finished. But the intensity of the battles in remote provinces such as Zabul, predominantly in the southeast, have revealed that the Taleban are still a force to be reckoned with, able to count on a steady supply of fresh recruits from the madrassas of Pakistan, where the religious movement was born.

Since the winter snows melted this spring and fighters came out of the mountains, hundreds of Afghans have perished in battles, assassinations and ambushes. Most of the dead have been guerrillas, in fighting that American commanders attribute to a more aggressive search-and-destroy campaign, but many other victims have been government officials and Afghan security forces attacked by the rebels.

Among the dead have been 37 American soldiers, making the past four months the bloodiest period for US forces since they invaded Afghanistan in late 2001 to oust the hardline regime from power. Commanders who just a few months ago were writing off the rebel force now say that the country should expect a further increase in violence before the parliamentary elections in September.

Although unable to capture and hold territory, the Taleban are now engaged in a fast-paced game of cat and mouse with American and Afghan forces, striking them when the opportunity arises while they pursue a campaign of intimidation against the local population.

The soldiers of the 2nd battalion, 503rd infantry, who arrived here four months ago, have been forced to alter their expectations radically. They are the first to admit that they are astonished by the tenacity of the fighters.

When American forces arrived in Miana Shin district late last month after reports that the Taleban had taken over the town, villagers told them that the guerrillas had warned them to get off the streets and shut up the bazaars because, in the words of one: “We are going to fight the Americans here.”

To the soldiers’ amazement, the Taleban kept up the battle for 12 hours, despite heavy bombardment from aircraft and helicopter gunships raining down artillery on them. “They fought for six or seven hours of airstrikes,” Sergeant Smith said, recalling how the fighters used AK47s and rocket-propelled grenades to try to shoot down the aircraft, hitting two Chinooks and a Black Hawk. “I’ve never seen them so aggressive. It was like Braveheart. They really believe they can shoot them down.”

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