American B-52 bombers tried their best to flatten Taliban field headquarters north of Kabul Friday in what may have been an attack directed by U.S. ground forces.

Later, a U.S. helicopter crashed in bad weather, injuring four crewmembers. The helicopter was on a special forces mission and all four crew members were rescued by another helicopter on the same mission, according to the Pentagon. 

F-14 Tomcats from the aircraft carrier USS Theodore Roosevelt destroyed the downed helicopter in order to prevent it from falling into the hands of either the Taliban or Al Qaeda. 

Meanwhile, U.S. forces narrowed their search for Usama bin Laden down to a handful of caves — possibly as few as 6, Fox News has confirmed.

The decision now is whether to launch a commando raid on those caves, or to drop "bunker buster" bombs into them.

The B-52 bombardment appeared to be part of a new, stronger push by the U.S. to help the opposition Northern Alliance make substantial gains against the Taliban before winter makes battle much more difficult.

Wave after wave of bombs fell from the U.S. sky fleet as elated opposition fighters and awed villagers on the opposition-held side of the front  tried to keep count. They estimated as many as 60 bombs fell, but lost track as huge explosions sent plumes of smoke surging up from Taliban positions.

"There are too many to count!" 20-year-old opposition fighter Sham Sher Khan said.

At the front Friday, Afghan opposition official Saeed Hussain Anwari said Americans were on the ground in opposition territory, and appeared to be directing the strikes on Taliban positions.

In Washington, U.S. Defense Secretary Donald H. Rumsfeld confirmed Thursday that a small number of U.S. special forces were on the ground helping to identify targets for U.S. warplanes and coordinating with the opposition. U.S. officials indicated the U.S. ground deployment was between 100 and 200 men.

"I'd like to see as soon as humanly possible the number of teams go up by three or four times," Rumsfeld said, saying the present size was "nowhere near as many as we need."

Taliban artillery gunners fired in vain at warplanes flying miles above. They also trained some of their guns on opposition forces across the front line, drawing return fire.

Afghanistan's opposition forces have moved more troops and artillery to the front. Heartened by the intensifying U.S. bombing, opposition fighters insist they are prepared to move on Kabul.

"We are ready for our orders," fighter Allah Udin said Friday.

Winter normally brings a lull to the fighting in Afghanistan, closing mountain passes and making many roads impassable, so Northern Alliance forces are pressing for a major push before the heavy snows.

The U.S., however, has called for patience — stressing that this could be a long war.

"We're still in the very, very early stages of this conflict," Rumsfeld said Thursday.

Rumsfeld was headed to Russia and Central Asia this weekend to shore up regional support for the offensive.

Across Taliban territory, other U.S. strikes were reported overnight at the Taliban's southern headquarters of Kandahar and at front lines surrounding their northern stronghold of Mazar-e-Sharif.

One huge bomb blasted the abandoned Qara Muheb village that opposition forces said the Taliban used as a field command center. To the south, more B-52s overflew Kabul, striking at the capital for the first time since Sunday.

Overnight, Taliban forces clashed with supporters of another influential anti-Taliban Pashtun leader who had slipped back into the country to rally support for deposed king Mohammad Zaher Shah.

The Taliban claimed tribal leader Hamid Karzai had escaped but 25 of his supporters were captured. Karzai's family in Pakistan confirmed the clash and said he was safe. The report of captured opposition supporters could not be confirmed.

Last week, a similar mission to mount opposition to the Taliban among southern Afghan Pashtuns received a severe blow when former guerrilla leader Abdul Haq was captured and hanged near Kabul.

Both Haq and Karzai sought to win support for a conference of Afghan leaders under the chairmanship of Zaher Shah to set up a new government to replace the Taliban.

U.N. Afghanistan envoy Lahkdar Brahimi was due in Iran on Friday for a round of talks on Afghanistan's future.

Brahimi and others are pushing for a future government that represents Afghanistan's range of ethnic groups and poses no threat to other countries.

The Associated Press contributed to this report.