The United Nations says thousands of refugees have fled Kandahar as tribal and other opposition fighters press for control of the Taliban's last bastion. 

Waves of U.S. warplanes pounded the southern Afghan city, which Taliban supreme leader Mullah Mohammed Omar has vowed to defend to the death. 

One Pashtun tribal commander claimed that hardline foreign Al Qaeda troops, loyal to prime terrorist suspect Usama bin Laden, were stopping demoralized Afghan Taliban troops from surrendering. Another tribal force said it had captured a tower near Kandahar airport and was determined to take the facility. 

U.S. military forces took into custody a man claiming to be an American. He was among more than 80 Taliban and Al Qaeda fighters who straggled out of a flooded basement days after their prison rebellion was crushed at an Afghan fort by the Northern Alliance in Mazar-e-Sharif. 

U.N. High Commissioner for Refugees spokesman Peter Kessler estimated that 8,000 Afghans have reached the safety of neighboring Pakistan since the conflict intensified last week. 

"It would appear that 2,000 people or more are leaving Kandahar province each day and are seeking assistance," Kessler said. 

Those who have arrived at the Pakistan border outpost of Chaman talked of chaos and fear in Kandahar as well as on the roads east to Pakistan. Conditions in and around Kanadhar were unclear Monday and reports of clashes among rival forces could not be verified. The Taliban refuse to allow foreign journalists into the areas they control. 

One refugee, Mohammed Nasim, said he saw the wrecks of half a dozen vehicles that had been apparently destroyed by U.S. bombing on the road from Kandahar to the border. 

Other refugees have fled north to the capital, Kabul. 

U.S. Marines stationed at a desert base about 70 miles southwest of Kandahar have not joined the fight since helicopter gunships attacked a Taliban convoy a week ago. 

A military source at the base said on condition of anonymity that the Taliban had moved reinforcements into Kandahar from Lashkargah, a town west of Kandahar. 

Arab satellite television Al-Jazeera quoted Mullah Obeid Allah, who governs a nearby Taliban-controlled town of Spinboldak, as saying Taliban forces had blocked some opposition fighters from advancing on Kandahar. 

In contrast, tribal forces said they had overcome and captured Taliban troops in the same area. The claims from either side could not be independently verified. 

Hamid Karzai, a powerful Pashtun tribal leader, said Monday his forces were 18 miles north of Kandahar and had met no resistance. 

"We have intentionally not launched any attack because we want to take the city without any fighting," he said by satellite telephone. 

"There have been some surrenders of Taliban soldiers," he said, adding that the backbone of the Kandahar's defenses appeared to be made up of mainly Arab Al Qaeda warriors. 

He claimed they were preventing Kandahar's Afghan Taliban force from capitulating. 

"They can't get out of the city to surrender. The Arabs have blocked the exits of Kandahar," he said. 

Nasim, who fled Kandahar on Sunday, said the city's Taliban fighters were playing a secondary role while its Arab defenders "believe in fighting to the death: no retreat. They have no other option, they have been backed into a corner." 

A tribal spokesman, Khalid Pashtun, said anti-Taliban forces, loyal to former Kandahar governor Gul Agha were moving from the south and east toward Kandahar and some fighters were near the perimeter of its airport and had captured a tower on Monday. 

"We have almost reached it," Pashtun said by satellite telephone. "Our forces are advancing. The Taliban and Arab forces are retreating from the airport." 

He predicted forces of tribal leader Gul Agha would seize the airport within a day or two. 

He said as many as 50 airport defenders died in overnight bombing, but said tribal forces had suffered no casualties. His report could not be confirmed. 

In Koenigswinter, Germany, Afghan delegates to U.N.-sponsored talks anticipated the elimination of the Taliban and continued to debate a blueprint for a broad-based administration to rule their country until a permanent government can be established. 

In Washington, Defense Secretary Donald Rumsfeld said U.S. forces would do "whatever is necessary" to root out Taliban and Al Qaeda fighters, including bin Laden, from cave hide-outs around Kandahar and in mountains in Afghanistan's east. 

U.S. bombing raids have concentrated on both regions for days. Anti-Taliban commanders near the eastern city of Jalalabad said some U.S. bombs have fallen on wrong areas, killing civilians and opposition fighters. 

A provincial security chief Mohammed Zeman said Monday that U.S. warplanes bombed a guesthouse in Agom village, 15 miles, south of Jalalabad, on Sunday evening. He said seven of his fighters and four civilians were killed. 

U.S. officials were not immediately available for comment. 

Earlier, Zeman said U.S. airstrikes had flattened an anti-Tailban headquarters in the same village on Sunday morning, killing eight people. Other Afghan officials said U.S. bombers destroyed a village nearby on Saturday. 

On Sunday, Air Force Lt. Col. Mark Compton, a Central Command spokesman in Tampa, Fla., said U.S. warplanes hit their intended targets around Tora Bora, the eastern cave complex that is a suspected Al Qaeda hiding place.