An Afghan National Police armoured vehicle patrols a street in Lashkar Gah, capital of Helmand province, on Wednesday. Two Nato soldiers were shot dead by uniformed men on an army base in the area, a stronghold for militants and opium.

AFP/Kabul

Men wearing Afghan military uniforms shot dead two Nato soldiers in the country's south on Wednesday, the coalition said, the first insider attack on foreign troops since the Taliban's bitter power transition.

So-called "green-on-blue" attacks - when Afghan soldiers or police turn their guns on international troops - have been a major problem during Nato's long years fighting alongside Afghan forces.

No group has so far claimed responsibility for Wednesday's attack in the volatile province of Helmand.

It was the first such incident since Mullah Akhtar Mansour was named the new Taliban chief following the announcement of the death of longtime leader Mullah Omar.

"Two Resolute Support (Nato) service members died early this morning when two individuals wearing Afghan (military) uniforms opened fire on their vehicle at an (Afghan security forces) compound in Helmand province," a Nato statement said.

"Resolute Support service members returned fire and killed the shooters," it added, without revealing the nationalities of the foreign soldiers.

The statement did not give the precise location of the attack, which highlights long-simmering tensions between Afghan and foreign forces.

Fierce mistrust

Western officials say most such incidents stem from personal grudges and cultural misunderstandings rather than insurgent plots.

The killings have bred fierce mistrust between local and foreign forces even though their number has declined in recent years.

The last insider attack was in April, when an American soldier was killed in a firefight between US and Afghan troops in eastern Afghanistan.

It was the first apparent "green-on-blue" attack since Washington announced a delay in US troop withdrawals from the country.

Nato ended its combat mission in Afghanistan last December and pulled out the bulk of its troops although a 13,000-strong residual force remains for training and counter-terrorism operations.

US Defence Secretary Ashton Carter at the time said the US soldier's killing showed that work remains to shore up Afghan forces in the "dangerous" country.

One of the worst insider attacks took place last August when US Major General Harold Greene was killed - the most senior American military officer to die in action overseas since the Vietnam War.

Nato troops have adopted special security measures in recent years to try to counter the threat.