KABUL, Afghanistan (AP) - A man in an Afghan army uniform turned his weapon on the American troops working with him in the country s east on Saturday, killing three of them, while an attacker with a grenade killed an Italian soldier in the west, officials said.

The shooting in Paktika province was the latest in a string of so-called "insider attacks" in which Afghan forces open fire on their own comrades or international troops. The incidents threaten to shake the confidence and trust of the two sides as the 2014 withdrawal of most of the international forces approaches.

An argument between the Afghan soldier and his trainers appeared to have led to Saturday s shooting on an Afghan National Army base in Paktika s Kher Qot district, according to a statement from the provincial governor s office.

The international military coalition in Afghanistan confirmed that three U.S. service members died in an insider attack but gave few other details.

The angry Afghan soldier opened fire during the argument, killing the three foreign trainers and wounding three others, according to the governor s statement. The foreigners returned fire and killed the Afghan soldier, who had no known connection to the insurgency.

So far this year, there have been five insider attacks on foreign forces, with a total of eight troops and one U.S. contractor killed.

Afghan security forces also are targets of such attacks. Last month, two recently rehired Afghan police opened fire on their commander at a checkpoint in a remote district in the country s south, killing him and six of his men.

The Taliban insurgents claim most of the insider attacks, saying they have infiltrated Afghan security forces or persuaded soldiers and police to join their side.

However, the international coalition has said many of them are sparked by personal disputes.

In the western province of Farah, meanwhile, an Italian soldier was killed and three others wounded when an attacker lobbed explosives into their armored vehicle in western Afghanistan, Italy s government said.

The Defense Ministry said the attack in Farah province came as the Italian soldiers were returning to their base from training Afghan security forces.

The Italian convoy of three armored vehicle apparently had been slowed by traffic near an intersection when an attacker ran up and threw an explosive device into the lead vehicle, the ministry said. It added that the three wounded soldiers  injuries were not life-threatening.

The Taliban quickly took responsibility for the attack, with spokesman Qari Yousef Ahmadi claiming that the attacker was an 11-year-old boy.

But Farah province provincial government spokesman Abdul Rahman Zhawandai says an adult man was seen throwing a grenade, then escaping by blending into the crowd at a nearby vegetable market.

Taliban insurgents have launched intense attacks across the country as Afghan forces take over most security responsibility ahead of most foreign troops  withdrawal next year.
Saturday s deaths brought to 16 the number of international troops killed in Afghanistan this month.