One US soldier was killed and a further two were wounded in southern Afghanistan on Tuesday, according to US military command in Kabul and NATO. According to NATO, the incident occurred in the southern Helmand Province, a traditional stronghold of Taliban militants.

"We are deeply saddened by this loss," said NATO spokesman Brigadier General Wilson A. Shoffner. "Our heartfelt sympathies go out to the families and friends of those involved."

Several Afghan troops were also wounded at the scene when a military helicopter carrying out a medical evacuation experienced "mechanical problems" after being grounded due to a nearby mortar explosion.

"It was not shot down," clarified Colonel Michael Lawhorn, another NATO spokesman with the mission in Afghanistan. Unconfirmed initial reports suggested the helicopter in question was a UH-60 Black Hawk.

According to US media, a group of US special operations troops came under mortar and small-arms fire during a counterterrorism mission and then the helicopter, a medical transport, was hit by mortar fire while it was on the ground.

The past six months in Helmand have featured increasing skirmishes between a resurgent Taliban and security forces. The deputy governor of the restive region warned in December that without further assistance the province could fall to the insurgents.

More than 2,000 US troops have been killed since NATO-led forces invaded Afghanistan in late 2001 following the September 11 attacks. After a protracted conflict that saw the Taliban give way to a democratic government of limited stability, foreign troops largely withdrew from the country in 2014.

Around 12,000 foreign servicemembers remain in the country however, largely in an advisory capacity. In the absence of NATO troops on regular combat missions, the Taliban has begun to reassert itself.

es/msh (AFP, Reuters)