In this photo shows US soldiers look out over hillsides in Afghanistan. File photo/AFP

Despite hopes that the conflict in Afghanistan was turning a corner, the Taliban has been holding on to large parts of the country and killing US and Afghan forces.

According to one report, American military leaders have periodically talked about their concerns about the war, particularly when seeking increases in troops or in capabilities needed to fight the Taliban.

Despite a winter lull in fighting due to heavy snowfall in the mountains where the militant Taliban typically rest and regroup ahead of their annual spring offensive, roadside bombs continue to hit Afghan forces and their foreign allies.

One such bomb hit a convoy of US troops on Saturday in Afghanistan's southern province of Kandahar, a NATO spokesman and an Afghan official said, but there were no immediate details of casualties in a blast claimed by the Taliban.

A senior Afghan military official in Kandahar said the incident took place in the district of Dand when the device hit one of the armoured vehicles of the US forces.

Foreign troops cordoned off the area and kept Afghan forces away from the scene, the official added.

The NATO spokesman said it was assessing the situation but declined to give details.

Taliban spokesman Qari Yousuf Ahmadi claimed responsibility for the attack and said the blast killed all the soldiers in the vehicle. The Taliban usually claim casualties and inflate figures when targeting Afghan and foreign troops.

Tens of thousands of Afghan civilians, members of the security forces and 2,400 US military personnel have been killed in fighting since 2001, when the austere regime of the Taliban was toppled by US and coalition forces.