The Taliban dug in for a grisly battle on multiple fronts Friday, as Northern Alliance forces and Pashtun tribesmen encircled two of their remaining strongholds at opposite ends of Afghanistan. Mullah Mohammed Omar, the Islamist militia's supreme leader, vowed to fight to the death and predicted "the extinction of America."

Although Omar continued to show defiance, several senior Taliban leaders were captured on Wednesday by Northern Alliance troops, a senior defense official told Fox News. The official said the U.S. is interested in the captives and may try to question the leaders in the hopes of finding out more about the location of Usama bin Laden or details on his Al Qaeda terror network.

As American warplanes made airstrikes supporting their movements, the alliance laid siege to the city of Kunduz, in an ethnically Pashtun area pressed up against the border with Tajikistan. Defending the city along with the Taliban were said to be an estimated 2,000 to 3,000 foreigners loyal to bin Laden.

Hundreds of miles to the south, the Taliban held on to Kandahar, the Pashtun city where the movement began in 1994. Hamid Karzai, an opposition leader, said Thursday that sources had told him there was "turmoil" in Kandahar; other sources said local anti-Taliban Pashtun tribesmen had surrounded the city and seized the airport.

A U.S. official, speaking anonymously, said there was sporadic fighting in the center of Kandahar as the tribesmen advanced. Most of Kandahar province was already held by anti-Taliban forces, the American official said.

Gen. Tommy Franks, commander of the U.S. campaign in Afghanistan, confirmed that American special forces were operating near Kandahar.

"We do see signs of some fracturing" within Taliban ranks, Franks said. "We are tightening the noose."

The rebellion by southern Pashtuns, members of Afghanistan's largest ethnic group and until this week the bedrock of support for the Taliban, illustrated how dire the militia's position had become.

The anti-Taliban Northern Alliance is mainly made up of Tajiks, Uzbeks and Hazaras, the country's other major groups. Large numbers of all groups live in Kabul, the capital.

Pakistan strengthened its border defenses closest to Kandahar with tanks and extra troops, worried that unrest — and bin Laden supporters — could spill across the frontier.

In other developments:

• Afghans on Thursday began their observances of Ramadan, the Muslim holy month. During five years of Taliban rule, Ramadan was a time of particularly harsh repression as Taliban religious police roamed the streets beating those who defied their edicts.

• Two young American women from a group of eight international aid workers arrested more than three months ago for preaching Christianity in Afghanistan gave their first public account of their ordeal Friday. The group was rescued by anti-Taliban troops in southern Afghanistan a day earlier and flown to safety by U.S. special forces.

• U.S. Homeland Security Director Tom Ridge confirmed that documents that would be helpful in making a nuclear device were found in a building in Kabul, described as an Al Qaeda safe house. But Ridge said the documents contained information taken off the Internet that could have been widely available to people other than terrorists.

• British troops arrived at the Bagram airfield, north of Kabul, on what the Ministry of Defense said was a mission to prepare the facility for use in a future humanitarian mission.

• In Washington, the Pentagon said some senior Taliban and Al Qaeda leaders were killed in airstrikes this week, but had no evidence bin Laden was among them. Defense Secretary Donald H. Rumsfeld told a news conference the United States will find bin Laden even if he leaves Afghanistan.

President Bush launched airstrikes against Afghanistan on Oct. 7 after the Taliban refused to surrender bin Laden, wanted in the Sept. 11 terrorist attacks on the World Trade Center and the Pentagon.

The Taliban supreme leader, Mullah Mohammed Omar, sought to portray the Taliban's recent retreats from urban centers as part of a larger strategy aiming to destroy America.

"If God's help is with us, this will happen within a short period of time — keep in mind this prediction," he said in an interview with the BBC, conducted over satellite phone. "The real matter is the extinction of America, and God willing, it will fall to the ground."

Omar ruled out taking part in a multiethnic government like the one the United Nations has proposed for Afghanistan.

"The struggle for a broad-based government has been going on for the last 20 years, but nothing came of it," he said. "We will not accept a government of wrongdoers. We prefer death than to be a part of an evil government."

Kandahar came under heavy bombardment Thursday, the Pakistan-based Afghan Islamic Press said. It said eight civilians were killed and 22 injured, a report that could not be independently verified.

In Quetta, Pakistan, across the border from Kandahar, an anti-Taliban Afghan source — speaking on condition of anonymity — said anti-Taliban forces had captured Kandahar's airport and urged that the Taliban hand over bin Laden. The source's claims could not be independently confirmed.

In the north, alliance commander Gen. Daoud said his forces wanted to persuade low-ranking Afghan Taliban in Kunduz to surrender. He said foreign forces in the city — believed to include Arabs, Chechens, Pakistanis and Chinese — were pressuring Taliban fighters not to surrender.

"For the foreign terrorists ... there will be no negotiations, we will not deal with them, they are killers," Daoud, who uses one name, said.

In preparation for a possible assault by the alliance, high-flying U.S. warplanes pounded Taliban troop and tank positions, with what witnesses said was deadly effect.

"On one hill there were a lot of Taliban, and after the U.S. bombs hit, there was nothing living there," said 20-year-old refugee Jaglan Mohammed Sakhay.

Outside the city, traffic was an incongruous mix of fleeing refugees, some of them barefoot women in burqas, and alliance fighters crowded onto truck beds, headed for the front.

With the Taliban abandoning Kabul on Tuesday, speculation has grown that Burhanuddin Rabbani, Afghanistan's president from 1992-96 and titular head of the Northern Alliance, will return to the capital.

Anwari, the Shiite Muslim Northern Alliance commander, said Rabbani was remaining for the time being in the Panjshir Valley, a staging ground for the alliance during its long anti-Taliban campaign in the north, because of the alliance's promise not to take power in the capital.

Meanwhile, the United Nations said its international staff was returning to Afghanistan, after being withdrawn soon after the Sept. 11 terror attacks in the United States. Spokeswoman Stephanie Bunker said five staffers had returned already and more were expected to do so soon.

In the western Afghan city of Herat, captured by the Northern Alliance earlier this week, many businesses were doing a brisk business Thursday in CDs and tapes that had been forbidden by the Taliban. Televisions and satellite dishes also were retrieved from hiding; residents watched live as Iran played Ireland for a berth in the World Cup soccer championship.

Just four months ago, Herat businessman Abdul Ahmed said the Taliban threw him in jail because they found a cassette tape on him.

"I was held for four days in jail. I was beaten so badly that you can't even imagine," he said.

The Associated Press contributed to this report