Thundering blasts, plumes of smoke and screaming warplanes over Taliban front lines north of Kabul on Wednesday testified to an intensifying U.S. air campaign to help the Northern Alliance oust Afghanistan's hardline Islamic militia.

In some of the heaviest bombing yet on the front lines, U.S. jets pounded Taliban positions north of the capital. Children and adults gaped at the skies, where U.S. planes — including what appeared to be B-52 bombers — roared throughout the day and into the night.

The Northern Alliance has repeatedly called for more intense and frequent U.S. air raids against the front lines, where it claims the Taliban have fortified their positions.

It's not clear if the latest raids will satisfy the opposition, which is betting on breaking the Taliban front lines to advance on the capital and other key areas, such as the northern city of Mazar-e-Sharif.

Both U.S. and Alliance officials say they're stepping up their coordination in the fight against the Taliban, which is under U.S. attack as punishment for harboring Usama bin Laden and the Al Qaeda terror network, accused of carrying out the Sept. 11 attacks in the United States.

Secretary of Defense Donald H. Rumsfeld acknowledged for the first time Tuesday that a "very modest" contingent of U.S. soldiers was in northern Afghanistan advising the opposition, coordinating resupply and helping direct U.S. airstrikes on Taliban targets.

On Wednesday, the sound of Taliban anti-aircraft fire echoed across the Shomali plain north of Kabul as American jets streaked across the sky. At one edge of the plain, in the foothills of the Safi Mountains, clouds of dust rose. Northern alliance soldiers said Taliban forces were moving their tanks in the area.

The Northern Alliance's deputy brigade commander in the Bagram district, Mir Rahman, said some U.S. planes were circling over the plain up to four times before dropping their bombs.

In the afternoon, two U.S. jets flying side by side dropped six bombs in the space of 10 minutes on Taliban positions on the front line, Alliance fighters said.

Four landed on Estarghich, sending a large cloud of dust over the Taliban-held village on the southwest side of the Shomali Plain, said Jamshid, a 21-year-old northern alliance fighter who like many Afghans uses one name. The two other bombs landed deeper inside Taliban territory, he said.

For the first two weeks of its military campaign, the United States largely avoided hitting the Taliban front lines. There were concerns that allowing the opposition to advance too quickly on the capital could pose a problem for Afghanistan's political future.

Northern Alliance leaders are mostly ethnic Tajiks and Uzbeks at odds with the country's majority Pashtun tribe. They earned many enemies when they were in power five years ago by plunging Afghanistan into factional infighting that killed 50,000 people in the capital alone.

U.S. jets began limited precision targeting of Taliban front line positions 10 days ago, escalating the attacks since last weekend. It's unclear exactly why the United States has shifted its focus to the front lines, but analysts say it may be related to recent failed attempts to persuade Pashtun leaders to abandon the Taliban.

Yet Alliance officials were still calling for stronger action.

"These planes have been bombarding the terrorists, and we haven't seen any positive results. Not even one small district has changed hands," Rahman said. "Why is there no success?"

There has been some speculation that the attacks would subside during the Muslim holy month of Ramadan, which starts in mid-November. But the commander of the U.S. operation in Afghanistan, Gen. Tommy Franks, remained noncommittal when asked Tuesday about a pause during a visit to Uzbekistan.

A fighter with the Northern Alliance's Zarbati commando units, Ghulam Rabbani, said Ramadan should not be an obstacle, saying even the Taliban have not honored it in past fighting with the alliance.

"Ramadan should not have any relation to the American attacks," he said. "If America stops bombing during Ramadan, the Taliban will take the opportunity to remobilize and resupply themselves."

"If they want us to fight during Ramadan, we will fight," Rabbani added.