US officials have revealed that an unknown number of US Special Forces have been either killed or wounded in Afghanistan's southern Helmand province.
The officials told US media that the forces were taking part in a counter-terrorism operation when they came under fire. According to the officials the incident took place near the city of Marjah.
A medical helicopter sent to rescue the casualties was then forced down.Some reports said the "medevac" helicopter had also come under fire.
A spokesman in Afghanistan for the US military confirmed it had landed, but said it was "experiencing mechanical malfunctions. It was not shot down. It intentionally landed safely."
US-led Nato combat forces left Afghanistan at the end of 2014, but training and special forces remain.
US special forces have recently been engaged in tackling Taliban fighters in Helmand.
Helmand has long been a stronghold of the Taliban.