By Frank Gardner BBC security correspondent at Bagram airbase

Aircraft from Bagram are lending close support to ground troops

Hundreds of US troops have been flown to the remote provinces of Nuristan and Kunar since Operation Mountain Resolve was launched last Friday.

So far, the only reported casualties have been amongst those whom the Americans call "anti-coalition forces".

Nearly every aircraft at Bagram airbase is taking part in the operation, along with other planes diverted from Iraq.

Tough terrain

Day and night the air here is filled with the roar of attack aircraft taking off, and the massed rotors of helicopters.

They're flying in to lend close support to US troops in the Hindu Kush mountains, as they struggle against freezing temperatures, high altitude and an elusive enemy.

US officials say they have been several gun battles over the last few days.

The casualties are thought to include militants linked to al-Qaeda.

A coalition spokesman, Colonel Rodney Davis, said this was the most challenging terrain American troops had fought over in Afghanistan.

He said they were doing all they could to isolate the enemy and slowly close the noose.

US reputation under fire

US officials in Afghanistan insist they are winning the war on terrorism here.

But in recent months there have been frequent attacks on coalition troops and a number of bombings in the south, an area where remnants of the Taleban appear to be gathering strength.

The coalition's reputation has also suffered from widely believed local reports that nine Afghans died in a US air strike in Nuristan at the end of October.

The US military denies the incident took place.