US special forces 'killed' and helicopter 'shot down' in Afghanistan

It is unclear whether the military aircraft was brought down by enemy fire

A number of members of the US special forces are said to have been killed (AP)

At least one US special forces soldier has reportedly been killed and others were wounded in Afghanistan - before the medical helicopter sent to rescue them came under fire.

NBC initially reported that the helicopter flying to pick up the wounded American soldiers had gone down after being hit. However, it subsequently emerged that although it was damaged, the military aircraft was able to take off.

CNN said the soldiers had been involved in a joint counter-terrorism operation in Helmand province with Afghan forces when they came under attack. An unknown number of people were also injured.

Officials said the US medevac chopper called in to recover casualties came under mortar and small-arms fire and was hit.

A spokesman for the Nato coalition in Afghanistan earlier told NBC News that a US helicopter had landed in Helmand province and was "experiencing mechanical problems."