KABUL: An Afghan army soldier turned his gun on his Nato colleagues on Monday injuring two US troops, officials said, just a day after a local policeman killed three foreign trainers in a similar attack.

The incident in the northern province of Faryab is the latest in a series of so-called “green-on-blue” attacks involving members of the Afghan national security forces targeting their Nato allies.

“An Afghan army soldier opened fire on US soldiers inside a military base... and injured two US soldiers. The attacker was killed in return fire,” Faryab's deputy provincial governor Abdul Satar Barez told AFP.

Nato's US-led International Security Assistance Force, to which most of the 130,000 Western troops in Afghanistan are attached, confirmed the incident but refused to give information on casualties.

“Operational reports confirm that an Afghan national army soldier turned his weapon on Isaf service members today in northern Afghanistan. Isaf troops returned fire killing the shooter,” an Isaf spokesman said.

“At this time there are no reports of Isaf fatalities.” The incident comes less 24 hours after an Afghan policeman killed three foreign civilian contractors working for Nato in the western province of Herat.

According to Afghan authorities the victims were helping Isaf train Afghan police.

Green-on-blue attacks have surged in recent months, resulting in 29 deaths.

Earlier this month, three British soldiers were shot dead by a man in an Afghan police uniform in the southern province of Helmand.

And last week an Afghan soldier was sentenced to death for killing five French soldiers in Kapisa province in January.

Taliban insurgents claim the attacks are carried out by insurgent infiltrators, but Isaf and Afghan officials say most such incidents are the result of cultural differences and friction between local and foreign forces.