A man wearing an Afghan security forces uniform has gunned down three international soldiers in the country's east, the NATO-led coalition said.
"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," a statement released by ISAF said on Saturday.
Afghan General Mohammad Zahir Azimi, a Defence Ministry spokesman, confirmed the incident, saying the attack took place in Gardez, capital of eastern Paktia province.
A US defence official reportedly told the Associated Free Press that the three victims were from the United States.
An Afghan official, speaking on condition of anonymity, also told AFP that the incident happened when an Afghan National Army (ANA) soldier opened fire on US soldiers in a military training camp, killing two on the spot, while a third later died of his wounds.
The attacker was killed when Americans and Afghan soldiers returned fire, he added.
A surge in insider attacks last year seriously eroded trust between the international coalition and their Afghan allies, and raised troubling questions about the unpopular war's direction.
The attack was the seventh such attack reported this year, and 12 ISAF personnel have been killed.
The last reported insider attack was on July 9, when an Afghan soldier at a military base in Kandahar shot dead one soldier and wounded three others.
ISAF officials say that most insider attacks stem from personal grudges and cultural misunderstandings rather than Taliban insurgent plots.
There are currently about 87,000 NATO-led troops fighting alongside about 350,000 Afghan security forces against the Taliban, in a war that has been going on since 2001.