An Afghan soldier was killed in a gunfight with US troops in southwest Afghanistan after he opened fire during an argument on Christmas eve, officials said on Sunday.

US troops were also injured in the incident on Saturday after the Afghan soldier began shooting and coalition troops returned fire in southwestern Farah province, Afghan army and police officials said.

"Last night in Bala Boluk an Afghan army soldier opened fire on foreign forces," said Najibullah Najibi, spokesman for the Afghan army in western Afghanistan.

"Four foreign forces have been wounded in this incident and the Afghan soldier has been killed."

A spokesman for the NATO-led International Security Assistance Force said there were no coalition fatalities but would not comment on ISAF casualties in line with policy.

"We are aware of the incident in... Farah province and we are still in the process of gathering all the facts. There were no ISAF fatalities," said Sgt Mike Montello.

Farah provincial police chief Sayed Mohammad Roshan Dil said "an Afghan army soldier opened fire on American troops".

"He was killed when American soldier returned fire. The firefight started after a quarrel," he said.

And district governor Mullah Ghawsedin said there was an armed clash in which at least one Afghan army soldier was killed after a dispute.

"We are investigating to find out what went wrong," he said.

NATO-led ISAF soldiers are in the process of handing over security to local forces before the scheduled withdrawal of all international combat troops by the end of 2014.

Coalition troops often carry out joint operations with Afghan army and police against the Taliban-led insurgency.