A US special operations soldier has been killed in fighting in southern Afghanistan on Tuesday, the US military said.
The battle against the Taliban took place in the district of Marjah in Helmand province, where the armed group has made significant recent gains.
One American soldier was killed and two others were wounded "while conducting a train advise and assist mission with their Afghan special operations counterparts", the Pentagon said.
"We are deeply saddened by this loss," said Brigadier General Wilson A Shoffner, an American military spokesman. "Our heartfelt sympathies go out to the families and friends of those involved."
A number of Afghan soldiers were also injured.
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The Pentagon said one of two helicopters sent to provide assistance came under fire, with one taking damage to its rotor blade and remaining on the ground.
Helmand is a traditional stronghold of the Taliban, which controls several districts.
Marjah is a strategic district in the south of the province. It is used as one of the main supply routes for Sangin district - situated in the north of Helmand - and has been the scene of heavy fighting between government forces and Taliban in the last few weeks.
Losing control of Marjah would deprive the Taliban of a vital supply route.
Afghan forces are battling to push out Taliban fighters who seized large swaths of the key, opium-rich district of Sangin in December.
Helmand's deputy governor in a post on Facebook asked President Ashraf Ghani for urgent intervention to save the province that British and US forces struggled for years to defend against the Taliban.
| Afghan and Taliban forces trade blows in Sangin battle
Source: Al Jazeera and agencies