Five NATO soldiers were wounded by a man dressed in an Afghan army uniform on Tuesday; they are now undergoing medical treatment.

NATO reported Wednesday that the attack occurred in Wardak province to the east of Kabul, an area that has seen an increase in Taliban attacks over the past year.

An Afghan witness named Eman told the Associated Press that he was there when the shots rang out.

The Americans were standing on the other side of us [Afghan civilians] while we were standing with a translator. Suddenly the Afghan soldier aimed his machine gun on them and started shooting, he said.

Eman was pulled to safety as the wounded soldiers were taken away in a helicopter. The assailant fled the scene, escaping through some trees and into a nearby village. Investigations into his whereabouts continue.

These so-called green-on-blue attacks -- in which agitators dressed in Afghan army uniforms inflict violence on NATO soldiers -- have been on the rise in recent months. On Monday, three British soldiers died when a man dressed as an Afghan police officer opened fire. Last month, three actual Afghan police officers carried out an attack that killed one U.S. soldier.

The Associated Press reports that 26 NATO troops have been killed so far this year in 18 such rogue assaults. Add in the number of soldiers killed in battle or insurgent attacks, and the total death toll for 2012 stands at 221.

According to NATO, about 129,000 foreign troops from over 50 different nations are currently serving in Afghanistan. These forces are working to equip and train the Afghan National Security Forces, which has about 164,000 members, so that it can maintain order and defend Afghanistan against insurgencies and other threats.

NATO hopes to officially end its mission there in 2014, though some troops will remain in Afghanistan as a stabilizing presence indefinitely.

NATO withdrawal was facilitated by Pakistan's decision, announced Tuesday, to once again allow NATO to transport supplies via its overland routes in landlocked Afghanistan; the route was closed in November of last year when U.S. airstrikes inadvertently killed 24 Pakistani soldiers.

The reopening will allow for increased ease of transfer so that NATO's planned departure can progress more smoothly. But violent attacks like Tuesday's shooting shed doubt on whether Afghan forces will be ready to take over national security by 2014.