A NATO soldier and a civilian contractor have been killed in a suspected insider attack in eastern Afghanistan, the latest in a series described by a top US general as "the signature attack" of the Afghan war.

The assault on Saturday night also resulted in Afghan army casualties, NATO's International Security Assistance Force said Sunday, without providing further details.

But police spokesman Abdul Wali told AFP that two Americans had been killed and three were wounded, while three Afghan army soldiers died and two others were hurt.

The deaths followed "a verbal dispute" during a joint operation in Sayedabad district of Wardak province west of Kabul, the provincial governor's spokesman Shahidullah Shahid told AFP.

A joint assessment of the incident by ISAF and the Afghanistan National Army is under way.

The scale of the so-called green-on-blue assaults is unprecedented in modern warfare, and has seriously undermined trust between NATO coalition forces and their Afghan allies in the joint effort against Taliban insurgents.

"I'm mad as hell about them, to be honest with you," top NATO commander General John Allen told CBS's "60 Minutes" programme recorded before the latest incident and scheduled to be aired Sunday.

"We're willing to sacrifice a lot for this campaign, but we're not willing to be murdered for it," the commander said, according to excerpts of the interview released by the network.

Allen said that just as homemade bombs had become the signature weapon of the Iraq war, he believed that in Afghanistan, "the signature attack that we're beginning to see is going to be the insider attack".

The latest death takes the total number of ISAF troops killed in 36 insider attacks this year to 52, accounting for about 15 percent of all coalition casualties in the war.

NATO attributes about 25 percent of the attacks to infiltration by Taliban insurgents into Afghan security forces while the rest are believed to result from cultural differences and personal animosities between the allies.

Efforts to combat the phenomenon include orders that NATO soldiers working with Afghan forces should be armed and ready to fire at any time, even within their tightly protected bases, and the issuing of cultural guidelines.

The guidelines, drawn up by the Afghan defence ministry, urge their soldiers not to take offence if NATO colleagues exit the shower naked, swear or ask to see pictures of their wives.

This is normal behaviour and no reason to open fire, the hastily written 28-page brochure says.

The assaults pose a serious threat to the NATO war effort, which has portrayed the advising and training of Afghan forces as the key to the scheduled pullout of Western troops.

Earlier this month, ISAF announced a scaling back of joint operations with its Afghan partners following a dramatic rise in such attacks, in which Afghan soldiers turn their weapons on their Western allies.

But US Defence Secretary Leon Panetta said on Thursday that troops had resumed most joint operations with Afghan forces.

Panetta vowed that the insider threat would not derail plans to transfer security to Afghan forces by the end of 2014, paving the way for the withdrawal of most NATO combat forces.

"We must and we will take whatever steps are necessary to protect our forces. But I also want to underscore that we remain fully committed to our strategy of transitioning to Afghan security control," he said.