GARDEZ, Afghanistan ? Afghan troops and tanks rushed to the battle zone Friday to bolster U.S.-led coalition forces against determined pockets of al-Qaida militants fulfilling their vow to fight to the death.

“I have not seen anyone surrender,” said Col. Frank Wiercinski, a brigade commander in the 101st Airborne Division.

U.S. officers say 500 to 600 al-Qaida and holdouts have been killed since Operation Anaconda began last week. The death toll is far higher than U.S. estimates of the size of the entire enemy force when the operation began.

The confirmed coalition toll remained at eight U.S. servicemen and three Afghans.

Fighting was intense Friday in the southern sector of the 60-square-mile area of operation was intense, Col. Joe Smith, chief of staff of the 10th Mountain Division, said at Bagram air base.

He said al-Qaida forces had suffered “lots” of casualties over the past 24 hours but gave no figure.

Heavy snow blanketed the region’s mountain passes, but ground and air operations pressed on, and the rumble of heavy explosions from the battle area could be heard more than 20 miles to the north.

With the fight intensifying, the interim Afghan government of Hamid Karzai rushed in reinforcements, bolstering an Afghan force made up largely of militias recruited by U.S. special forces.

The central government was sending about 1,000 new Afghan fighters to the Gardez area, of whom about 600 had already arrived, said town council member Safih Ullah. They were under the command of Gul Hydar, backed by tanks and other fighting vehicles.

A convoy of 12 to 15 tanks was seen in Logar province Friday heading south from Kabul to Gardez. An Associated Press photographer saw another convoy including trucks carrying multiple rocket launchers and other vehicles with soldiers armed with rifles and grenade launchers headed toward Gardez from Kabul.

The need for reinforcements became apparent after U.S. commanders, relying heavily on their Afghan partners, underestimated the size of the al-Qaida force.

Afghan fighters said they were told to expect about 100-150 al-Qaida foes.

Americans wounded during recent operations gave a picture of how tough it is to uproot the hardened fighters from their mountain positions.

The three members of the 10th Mountain Division  speaking to journalists at a base in Landstuhl, Germany, where they were recuperating  said more than 100 American troops were pinned down by al-Qaida fire Saturday in a valley until helicopters pulled them out under cover of darkness.

The soldiers were hit by bullets or mortar rounds from enemy fighters who they said were perched on overlooking ridges and ducked into caves to defy U.S. bombers’ and helicopters’ attempts to dislodge them.

“We’re fighting in their back yard,” added Spec. Ricardo Miranda, 20, of Salinas, Calif., whose right arm and left leg were heavily bandaged. “They know where every crack in that mountain is, every cubbyhole, every cave.”

In Washington, Defense Secretary Donald H. Rumsfeld said the offensive could end as early as this weekend. However, he said al-Qaida was also rushing in reinforcements and supplies.

“We have seen some infiltration of additional fighters in small numbers, traveling in SUV’s from the south,” Smith said.

Wiercinski said that seven days into the operation, U.S. troops were no longer seeing large groups of fighters. “They are determined. Whether you would call that martyrdom or whatever, they are still determined in their small pockets,” he said.

Special forces teams established checkpoints along roads and smuggling routes to try to intercept al-Qaida fighters trying to slip in from the area along the Pakistani border.

An Afghan commander, Abdul Matin Hasankhiel, said some al-Qaida sympathizers managed to cross the Pakistani border early in the battle but he thought most had been blocked.

Other Taliban and al-Qaida supporters were believed responsible for two attacks this week in nearby Khost: a shooting attack on U.S. forces at an airstrip and a bomb blast that destroyed a music and video shop, local official Mohammed Ibrahim said.

Hafeezullah, member of the Surmad town council, said men from his region probably joined to fight with al-Qaida because of the prestige of the local commander, Saif Rahman, a former Taliban official whose family comes from the area.

Rahman issued a call earlier in the week for jihad, or holy war, against the U.S. campaign and had sworn to fight to the death.

Meanwhile, the Pentagon is sending about 200 soldiers from the 101st Airborne Division at Fort Campbell, Ky., equipped with 16 Apache helicopters and four CH-47 Chinook helicopter transports. About 107 members of a Canadian infantry unit are also on the way.

Smith said documents uncovered during the battle have showed that the besieged al-Qaida fighters “are highly trained military soldiers.”

Documents found by coalition troops conducting cave-to-cave searches have shed light on al-Qaida’s use of heavy weaponry, including mortars, small cannons, rocket-propelled grenades and shoulder-fired anti-aircraft missiles.

Still, Smith said the militants were surprised when the offensive was launched March 1.

“I think they believed that we were going to fight them head on and we hit them in the rear. And even though they knew for seven or eight days that we were going to attack, they just didn’t know where or exactly when,” he said.