The Taliban's opposition said they were closing in on a key northern city Wednesday with the help of the U.S. bombing campaign.

The northern alliance said they had captured a district near Mazar-e-Sharif from Taliban forces and were about to capture the city.

Opposition troops took control of Shol Ghar district, about 30 miles from Mazar-e-Sharif, and some units were just eight miles south of the city, said northern alliance spokesman Ashraf Nadeem.

The Taliban denied they had lost Shol Ghar and said they would move 500 fresh fighters into the area by Thursday despite raids by U.S. warplanes.

A Taliban official said the opposition was lying and that its claims were baseless, the Pakistan-based Afghan Islamic Press reported. It did not identify the official.

It said the official, speaking in the eastern city of Jalalabad, acknowledged opposition forces had earlier seized Zaray -- one of three districts south of Mazar-e-Sharif that the opposition said it controlled Tuesday after a pre-dawn attack.

The Taliban captured Mazar-e-Sharif in 1998, and losing it would seriously weaken the Islamic militia's position in northern Afghanistan.

U.S. jets played a critical role in Wednesday's opposition advance, targeting several pickup trucks packed with departing Taliban troops as well as hitting fortified positions, Nadeem said by satellite telephone.

U.S. warplanes also bombed behind Taliban positions on the Kabul front Wednesday. Witnesses said they heard no anti-aircraft fire from Taliban fighters, who have periodically tried to shoot down U.S. jets since the bombing began exactly a month ago.

American jets dropped dozens of bombs late Tuesday and throughout the day Wednesday around positions about 30 miles north of Kabul, the capital. Some explosions were followed by up to 30 smaller detonations.

One blast sent up a huge streak of gray smoke that spread into a white mushroom cloud. U.S. planes circled overhead.

An opposition commander, Qand Agha, 30, said a U.S. jet hit a Taliban tank northeast of Kabul and that a B-52 bomber dropped 20 bombs around the front line in one hour Wednesday afternoon.

"It is improving but it is not enough," Agha said of the bombing. "I would like to see the Americans drop at least 200 bombs a day."

Abdul Maaruf, a 17-year-old opposition fighter with blue, sparkling heart stickers decorating his Kalashnikov, said Taliban artillery fire had diminished in recent days, possibly because gunners were choosing to hold their fire.

"If they don't see any planes, they fire on us," Maaruf said. Taliban trucks have recently arrived with supplies, he said.

Agha said the Taliban were saving their ammunition, possibly expecting an opposition offensive. Four of his fighters watched the front from a rooftop lookout while the other dozen members of the unit played volleyball as the sun set over the plain.

A warmer spell was melting snow on the surrounding Hindu Kush mountains, and opposition fighters said trucks might be able to cross again soon, at least until the next snowfall. But they predicted the passes will snow over by the end of the month, choking off supply routes until spring.

In villages surrounding Jabal Saraj, about 45 miles north of Kabul, fliers that witnesses said were jettisoned from a B-52 bomber tumbled from the sky. Children and adults scrambled to pick them up.

The fliers showed a picture of a radio and antenna, and detailed times and frequencies for radio broadcasts in the local Pashtun and Dari languages. The United States has been broadcasting anti-Taliban statements into Afghanistan.

The Taliban's Bakhtar News Agency said bombs north of Kabul, in the eastern city of Jalalabad and the western city of Herat on Tuesday and Wednesday killed at least 23 people and injured several dozen others. The report could not be independently confirmed, and the Pentagon has denied Taliban claims of widespread civilian casualties.

Bakhtar said that U.S. planes dropped food packets before launching bombing raids, but that angry residents burned the aid.

At the Pentagon, Defense Secretary Donald H. Rumsfeld said Tuesday that an assessment of the opposition claims of gains outside Mazar-e-Sharif would have to wait until the "dust settled."

But after seesawing battles south of the city in recent weeks, the opposition said intense strikes by American planes had opened the way. The alliance had complained earlier that U.S. bombing was not heavy enough.

Nadeem said 500 Taliban soldiers had crossed over to the opposition side. The Taliban have previously denied reports of defections from its ranks.

The northern alliance's key Shiite Muslim commander, Mohammed Mohaqik, said Wednesday he wanted the assault on Mazar-e-Sharif to be carried out in a way that would minimize civilian casualties. Mazar-e-Sharif has a large Shiite Muslim population, although its majority is ethnic Tajik.

"We have to make plans over the next two days as to how to take Mazar-e-Sharif, to reduce the number of casualties," he said. "But it's a war, and with exchange of artillery fire and rockets, people will die."

The Pentagon has said small numbers of American special forces teams are working with northern alliance forces to train and equip them, provide them with additional ammunition and weaponry, and identify targets for U.S. strike aircraft.

But with winter is closing in, bad weather could choke off supply routes for troops. The Pentagon says it intends to start delivering cold-weather clothing to the northern alliance.

President Bush launched airstrikes against Afghanistan on Oct. 7 after the ruling Taliban militia refused to hand over Usama bin Laden for his alleged role in the Sept. 11 terrorist attacks on the United States.

On Tuesday, Bush pledged "to keep relentless military pressure" on bin Laden and the Taliban, saying it is essential to keep terrorists from acquiring nuclear, chemical and biological weapons.

The Associated Press contributed to this report.