GARDEZ, Afghanistan ? U.S.-allied Afghan fighters massed near the mountains of eastern Afghanistan on Monday, rumbling up the desolate peaks in tanks and trucks before a sweeping push to clear out al-Qaida fighters hiding out in the region’s warren of caves.

The United States resumed steady bombing runs over the area after nightfall Monday.

In Washington, Secretary of State Colin Powell described the fighting as a “mopping up” operation after more than a week of heavy bombing and ground combat. Afghan commander Mohammed Ismail Khan estimated that three-fourths of the enemy force had been destroyed.

Defense Secretary Donald H. Rumsfeld, speaking Monday in front of the Pentagon, said Operation Anaconda here in Paktia province would continue “until it’s completed.”

Rumsfeld said “a great many al-Qaida” members had been killed and “several prisoners” had been taken. “As the mopping up process continues, additional information will be gained,” he added.

The apparent winding down of Operation Anaconda coincided with ceremonies six months after the Sept. 11 terror attacks, which triggered America’s war on global terrorism.

A convoy of at least 12 tanks and about 1,000 soldiers moved Monday toward the front line to reinforce hundreds of American troops believed still in the Shah-e-Kot mountains as part of the largest offensive yet in the Afghan war. U.S. Special Forces were seen operating at the base of the mountains.

Afghan commanders quoted American officers as saying they preferred to soften up the remaining enemy force even further before trying to overrun their last positions.

Hundreds of U.S. troops from the 10th Mountain Division and the 101st Airborne Division were rotated back to their bases last weekend after hostile firing had died down.

“The al-Qaida and Taliban extremists seem to be in much smaller pockets now not the larger groups that we saw the first few days,” said Maj. Bryan Hilferty, a spokesman for the 10th Mountain Division. “We will continue to work our way through the area until we are satisfied we have taken out all of the al-Qaida terrorists.”

Hilferty declined to say whether Special Forces had actually entered any of the Taliban and al-Qaida caves.

At Bagram air base, Sgt. Jose Roman, a former New York City policeman, said he had been waiting to strike back ever since Sept. 11.

“This mission is very important especially for me,” he said.

Although fighting has subsided, troops returning from battle said the early stages were marked by intense combat. Pfc. Jason Ashline, 20, of New York, said he was shot twice but survived because the rounds lodged in his bulletproof flak vest.

“For a couple of seconds, everything was, like, in slow-motion,” Ashline said. “I was pretty scared because I didn’t feel no pain. I thought, ‘what’s wrong?’ I thought maybe I was dead.”

Lt. Adam Hall, 24, a platoon leader of the 101st Airborne Division from Charleston, S.C., said the fighting “was pretty scary” but the worst part of the experience was the bitter cold.

“The nights were our demons,” said Spc. Brian Schuett, 24, of Cuyahoga Falls, Ohio. “That’s when it got really cold, and it snowed up in the mountains. Every night there were planes going over you, bombing. You were lucky if you got an hour of sleep.”

The leader of Afghanistan’s interim government, Hamid Karzai, had ordered fresh troops to the region, which he called the “last main base” of al-Qaida and Taliban in Afghanistan. He acknowledged, however, that there are areas where smaller groups are likely operating.

Khan, the Afghan commander, said the al-Qaida forces are weak but reaching them is a problem because land mines surround their positions. Forces on the ground are counting on superior air power to help finish the fighters off.

“We don’t know how many are still alive,” Khan said. “The bombing has been so strong I don’t know how anyone can survive.”

Another commander, Haji Nawab Zardran, said U.S. forces were on the front lines clearing mines. Afghan fighters have insisted the bulk of the force was made up of non-Afghans fighting for al-Qaida. U.S. troops back from the front said they were too far from their enemy to determine whether they were Afghans or foreigners.

Operation Anaconda was launched March 2 to crush al-Qaida and Taliban forces in the mountains of Paktia province.

Soldiers returning for the front lines suggested that the bombardment was taking its toll on the al-Qaida forces. Lt. Col. Chris Bentley, 38, of Nacogdoches, Texas, said air power either neutralized or destroyed at least 20 cave complexes.

It took only five minutes for fighter planes and attack helicopters to hit a target after a soldier on the ground called the target in, he said.

“We hope none are left,” he said.

Ismail said that in the past two days, Australian commandos and vehicles had been dropped into the battle area, presumably to search for small pockets of al-Qaida members who might try to slip away through narrow gorges.

Hilferty said some enemy fighters had been captured and were being interrogated, but he declined to say how many.

One captured Arab fighter claimed other Arabs, Tajiks and Uzbeks were still in the caves and that the tunnels had collapsed in the bombing, Afghan intelligence officials said on condition of anonymity.

Meanwhile, Ishaq said the brother of a former Taliban commander has surrendered to Karzai’s government. Ibrahim Haqqani is the brother of Jalaluddin Haqqani, who was known for his close ties to the al-Qaida network in Paktia, the region where the U.S.-led offensive is taking place.

Ibrahim Haqqani met with U.S. officials in Kabul, but it was not immediately clear if he provided information about al-Qaida concentrations and bases in the region.

Meanwhile, hundreds of masked gunmen manned checkpoints in the eastern town of Khost to search for weapons, the Afghan Islamic Press reported. The gunmen have also forced shops and markets to close as part of the massive search.

The operation came a day after attackers killed four men from the Zadran tribe led by warlord Bacha Khan, who is leading an Afghan militia fighting alongside U.S. troops.

Khost is on the southeastern end of the battle area and is close to the Pakistani border. The area, a hotbed of support for the Taliban and al-Qaida, has been the scene of several sporadic bombings and shootings since the U.S.-led operation began eight days ago.