The two special forces Chinook helicopters had come in, unfortunately, at sunset. They were racing to rescue their comrades on the ground. Onboard the lead chopper--a giant, twin-rotor beast called an MH-47--were eight Navy SEALs and an eight-man Army flight crew. The SEAL commandos, part of a supersecret task force hunting down "high value" Qaeda and Taliban fugitives, were searching for a lost reconnaissance team in the treacherous Kunar border region of Afghanistan. The recon team had been ambushed in the heavily forested mountains in midafternoon on June 28, apparently by Taliban fighters who may have been protecting the wanted rogue Afghan commander Gulbuddin Hekmatyar.

But the timing of the rescuers' arrival, at dusk, turned the Chinooks into fat targets: noisy black shapes silhouetted against a glowing western sky. And apparently the enemy was waiting. As the helicopters lumbered overhead near the Afghan town of Asadabad, they encountered heavy fire from the ground. A guerrilla launched what is believed to be a rocket-propelled grenade, hitting the lead Chinook's fuselage, according to multiple military sources. Two Apache attack choppers and a pair of A-10 Warthog jets overhead were flying shotgun, but they could do nothing. As the other aircraft crew watched in horror, the pilots on the lead Chinook struggled to regain control. The Chinook finally crashed on the edge of a ravine, then rolled over the lip and down a steep slope, according to Pentagon briefings. In all, 16 U.S. soldiers onboard died.

The fate of the recon team they'd been sent to recover was still uncertain late last week. But chillingly, the newly emboldened Taliban announced they had also ambushed and executed seven American "spies," and had taken one American prisoner. The report could not be confirmed. U.S. officials said an unmanned Predator scout plane--also part of the mission dubbed Operation Red Wing--had been lost as well.

Whatever the final death toll, the Chinook downing marked the single worst setback to American forces in Afghanistan since 2001. It was also a wrenching wake-up call. For a year now, as the insurgency in Iraq has raged, the Bush administration has been relatively pleased with its success in stabilizing Afghanistan. But last week's bloody encounter at Asadabad suggests that the situation is still very dicey, and perhaps getting worse. The Taliban, the exiled Islamist government of Afghanistan that is still seen as the main protector of Osama bin Laden, seems to have been regrouping rather than withering away. A fresh wave of Taliban guerrilla violence in Afghanistan this year has left more than 600 people dead, including 29 U.S. servicemen and more than 130 Afghan government soldiers.

According to one guerrilla commander, Mullah Salar Haqyar, the Taliban are increasingly confident and growing in numbers. In an interview, Haqyar said they have reached a three-year maximum of 500 to 600 fighters in Kunar alone. "As Kunar was the stronghold of jihad versus the Russian communists," he said, "thank God it is the same against the Americans right now."

The failed U.S. mission at Asadabad does bear haunting reminders of the humiliation of the Soviet Army in the same mountains during the 1980s. Milt Bearden, a former CIA officer in the region, says that CIA-supplied mujahedin--the forerunners of the Taliban--destroyed an entire Soviet Special Forces battalion at Asadabad in 1988. The mujahedin also succeeded back then because they could move back and forth across the Pakistani border into the nearby havens of Chitral and Dir.

Pakistani officials say they are helping as much as they can. But Pakistani military commanders also point out that with elevations in the area ranging from 9,000 to 15,000 feet, it is all but impossible to close off the border. And that may bode a long fight for American forces seeking to avenge their lost comrades--and, eventually, to come home.