A soldier with NATO's US-led coalition in Afghanistan was killed by a man in Afghan army uniform on Sunday, a spokesman for the mission said, in the latest so-called "green-on-blue" attack.

The death takes the number of foreign troops killed by Afghans they were working with to at least 19 this year, in at least 13 separate attacks.

"An individual wearing an Afghan National Army uniform turned his weapon against coalition service members in southern Afghanistan today, killing one service member," NATO'S International Security Assistance Force (ISAF) said.

"The individual who opened fire was killed when coalition forces returned fire."

ISAF, which does not list its wounded in any attack, gave no further details and said the nationality of the dead soldier would be announced in his home country.

The shooting is the latest in an increasing number of attacks by Afghan soldiers turning their weapons against NATO troops who are helping Kabul fight a decade-long insurgency by hardline Taliban Islamists.

Some of the assaults are claimed by the Taliban, who say they have infiltrated Afghan army ranks, but many are attributed to cultural differences and antagonism between the allied forces.

Little more than a week ago, an American soldier, two Afghan troops and an interpreter died when an Afghan special forces soldier opened fire on his US allies in the southern province of Kandahar.

In a separate attack on the same day, two Afghan policemen turned their weapons on US troops at a military post in the same province. No ISAF troops were killed, but both attackers were shot dead in return fire.

ISAF, which is training Afghans to take responsibility for security for the whole country by the end of 2014 when most foreign troops pull out, has said the green-on-blue deaths sap spirits among its soldiers.

"Although the incidents are small in number we are aware of the gravity they have as an effect on morale," ISAF spokesman Brigadier General Carsten Jacobson said in Kabul.

Among new measures taken to avoid similar incidents, Afghanistan's intelligence services are hiding agents among recruits at the country's army and police training schools to try to spot potential killers, NATO said.

ISAF has also taken several security measures in response to the shootings, including assigning "guardian angels" -- soldiers who watch over their comrades as they sleep.

Relations between the US and its Afghan allies have also been rocked this year by incidents involving American troops.

A video emerged of US forces urinating on Taliban corpses, copies of the Koran were burnt on a major US military base and an American sergeant has been charged with 17 counts of murder over a massacre of civilians.

ISAF has around 130,000 soldiers fighting alongside some 350,000 Afghan security personnel in a bid to help President Hamid Karzai's government reverse the Taliban-led insurgency.

In a separate statement Sunday, ISAF announced that one coalition service member died in a roadside bomb attack in the east of the country, without giving any further details.