GARDEZ, Afghanistan ? Airstrikes from American B-52 bombers shook the ground Thursday in some of the heaviest bombing of a six-day battle against tenacious al-Qaida fighters. The United States rushed in reinforcements and said 100 militants had been killed the previous day.

U.S. and allied Afghan soldiers were moving forward under al-Qaida fire, taking some ridges and caves in the mountainous region of eastern Afghanistan, said Maj. Bryan Hilfery, spokesman for the 10th Mountain Division.

U.S.-led infantry units have cleared out several cave hide-outs and al-Qaida compounds, including some where troops found AK-47 ammunition, medicine, night-vision devices and documents, including a Saudi identification card.

Hilfery said coalition forces killed at least 100 al-Qaida fighters Wednesday, but he had no word on new coalition casualties.

Eight American and three allied Afghan troops have died since Operation Anaconda began March 1.

Also, five international peacekeepers  two Germans and three Danes  were killed late Wednesday in Kabul while trying to defuse a Soviet-era missile left by the Taliban. Eight peacekeepers were injured in the first fatal accident since the force, which is separate from the U.S. military operation, was deployed to Kabul in December.

Throughout Thursday, thunderous blasts from B-52 bombers shook the mountains southwest of here. Dozens of Army Apache attack helicopters, armed with 30mm guns and Hellfire missiles, pounded targets in the narrow, craggy gorges.

The air bombardment, felt in Gardez at least 30 miles to the north, appeared heavier than in recent days as the United States accelerated efforts to crack the al-Qaida resistance.

Storm clouds moved in over Gardez in the afternoon and sandstorms whipped up, indicating possible snow in the mountains. Three Chinook helicopters flew into the key target area of Shah-e-Kot on supply missions under low cloud cover, but the worsening weather could hamper further action by the Apaches.

Afghan commander Ismail Khan said a U.S. special operations unit moved into the battle area Wednesday.

“There are 5,000 soldiers collecting in Shah-e-Kot for a final offensive on the al-Qaida to finish them off,” said Khan. “It will be the final push.”

Facing the allied soldiers is a force believed made up of Arab and other foreign fighters from al-Qaida, along with some of their Afghan Taliban allies. They are armed with mortars, small cannons, rocket-propelled grenades, shoulder-fired anti-aircraft missiles and Kalashnikov rifles.

Throughout the night Wednesday, U.S. transport helicopters shuttled between Bagram air base north of Kabul and the battle to the south, bringing in fresh supplies of food, fuel and ammunition.

In southern city of Kandahar, three U.S.-allied Afghan fighters were killed Thursday when one of them apparently accidentally tripped a booby trap at their own ammunition depot, a top Canadian officer said. Afghan forces said the men were moving a crate at the depot that they hoped to break down into firewood, said Lt. Col. Pat Stogran, commander of the 750 Canadians at the Kandahar air base. The depot is about a mile south of the base.

Canadian troops went to help, Stogran said, but shrapnel and other ordnance screamed over their heads. Detonations from the weapons depot continued into the evening and started a large brush fire.

Gen. Tommy Franks, commander of U.S. forces in Afghanistan, said in Washington the number of Americans in the operation grew by 200 to 300 over the past two days, for a total of roughly 1,100. They joined about U.S.-backed 1,000 Afghan fighters and a small number of elite, special operations troops from six nations.

“I think the days ahead are going to continue to be dangerous days for our forces,” Franks said in Washington. He raised the possibility sending in even more firepower, including additional transport aircraft, infantry and special operations troops.

Front-line commander Abdul Matin Hasankhiel said the battle to break al-Qaida was taking longer than expected because of the difficult terrain facing coalition troops.

“These are very high mountains and former mujahedeen bases that the Russians couldn’t defeat  even with their heaviest bombing and best soldiers,” he said, referring to the war against the Soviets in the 1980s.

U.S. estimates of enemy strength appeared to have been low going into the offensive. Initially, U.S. estimates put the size of the force at 150 to 200 fighters. Subsequently, U.S. officers revised those numbers to “the neighborhood of 600 to 700 enemy.”

The commander of the operation, Maj. Gen. Frank L. Hagenbeck, said more al-Qaida and Taliban fighters had infiltrated the 60-square-mile area battle zone to join the battle.

Earlier in the week, the Afghan Taliban commander in the hills, Saif Rahman, issued a call for jihad, or holy war, against coalition forces, saying it was the first responsibility of Muslims.

Franks said there was no sign of dug-in al-Qaida and Taliban fighters trying to flee the region  which commanders say they have encircled.

However, as recently as Tuesday night, Taliban holdouts brought the bodies of five slain fighters from Shah-e-Kot to the village of Surmad in the foothills for burial, said shopkeeper Abdullah Jan, who was in Surmad on Wednesday.

When asked how the Taliban could sneak by the allied forces blocking the mountain paths, he said: “There are hundreds of smuggler routes,” across the rugged terrain.

Afghans say neither the former Taliban supreme leader Mullah Mohammed Omar nor al-Qaida chief Osama bin Laden is in the area.

French Defense Minister Alain Richard said Thursday there was “a good chance” that bin Laden was dead. He didn’t elaborate in an interview on Europe-1 radio.

A local Afghan commander, who goes by the single name Isatullah, said U.S. forces received enemy estimates from an Afghan military leader from a different region who was unfamiliar with the territory.

Operation Anaconda is aimed at crushing al-Qaida fighters who came to this area after the collapse of Taliban rule last year.