KABUL: A man in Afghan army uniform opened fire on Nato soldiers at a military base near Kabul, wounding five, the coalition said Wednesday, the latest in a series of so-called “green-on-blue” attacks.

Attacks by Afghan security forces on their allies from the US-led alliance have claimed 26 lives so far this year, according to an AFP tally, with the latest incident taking the total number of such attacks this year to 19.

“An individual wearing Afghan army uniform turned his weapon on coalition soldiers yesterday (Tuesday), wounding five,” Colonel Jimmie Cummings, a spokesman for the 130,000-strong US-led Nato coalition force said.

“The wounded coalition soldiers were evacuated to a medical facility.” Dawlat Waziri, an Afghan defence ministry spokesman, confirmed the incident in Maidan Wardak province, a troubled region south of Kabul and said the attack took place inside a military base shared by Afghan and Nato troops.

“A man wearing our army uniform opened fire on the coalition soldiers, wounding five soldiers. The attacker fled the area and we're investigating the incident,” Waziri said. An increasing number of Afghan troops have turned their weapons against Nato colleagues helping them fight a decade-long Taliban insurgency.

The militants claimed the latest attack, with spokesman Zabihullah Mujahed saying the gunman was an “infiltrator” - an insurgent who enrolled to later attack from within.

But many attacks are attributed to cultural differences and antagonism between the allied forces.

On Monday a man in Afghan police uniform opened fire on his Nato mentors in the southern province of Helmand, killing three British soldiers.

That followed a similar incident two weeks earlier in which three Afghan police together turned on their Nato allies, killing one US soldier.

The spike in the “green on blue” attacks has prompted Nato to boost security measures while working together with their Afghan counterparts. The measures include assigning “guardian angels” - soldiers who watch over their comrades as they sleep.

The coalition is to hand over security to local forces by mid-2013 and will play a support role up to the final withdrawal by the end of the following year.