An Afghan Army soldier has shot dead three occupying US soldiers in the eastern part of the country, the NATO coalition said on Saturday.

An Afghan Army soldier has shot dead three occupying US soldiers in the eastern part of the country, the NATO coalition said on Saturday.

So-called "insider attacks", in which Afghan forces kill occupying NATO troops, have increased in Afghanistan.

"Three International Security Assistance Force (ISAF) service members died when an individual wearing an Afghan National Security Forces uniform shot them in eastern Afghanistan today," an ISAF statement said, adding that both ISAF and Afghan officials were investigating the incident.

A US defense official confirmed to AFP that the three victims were from the United Sates.

An Afghan official said that the incident happened during a training session in the eastern province of Paktia.

An Afghan National Army (ANA) soldier opened fire on US soldiers in a military training camp, killing two on the spot, he said. A third later died of his wounds, he added.

The attacker was killed when Americans and Afghan soldiers returned fire, he said.