A man wearing Afghan uniform shot dead three US soldiers today in the east of the country, officials said, in the latest apparent example of an "insider attack".
The strike came on the same day that one Italian soldier was killed and three others were wounded when a grenade was thrown into their armoured vehicle in the western province of Farah.
Scores of foreign soldiers have been killed in insider attacks, breeding fierce mistrust and threatening to derail the process of training Afghan forces to take over security duties ahead of NATO's withdrawal next year.
The threat has become so serious that foreign soldiers working with Afghan forces are regularly watched over by so-called 'guardian angel' troops to provide protection from their supposed allies.
There was no immediate claim of responsibility, but NATO officials say that most insider attacks stem from personal grudges and cultural misunderstandings rather than Taliban insurgent plots.
"Three ISAF (International Security Assistance Force) members were killed when an individual wearing ANSF (Afghan National Security Force) uniform turned his weapon on them and opened fire," a spokesman told AFP.
ISAF said on its Twitter feed that it was "investigating a possible insider attack in eastern Afghanistan".
Military officials in Kabul confirmed that the three dead soldiers were from the United States.
Local officials in the province of Paktika said that the incident had taken place in the district of Khair Kot.
"There has been an attack by a suspected member of the Afghan forces targeting NATO soldiers," Mukhlis Afghan, the spokesman for Paktika's governor, told AFP.
The Taliban launched their annual spring offensive at the end of April, marking a crucial period for Afghanistan as local security forces take the lead in offensives against the insurgents.
The Islamist militants said multiple suicide bombings and insider attacks by Afghan soldiers on NATO-led troops would be used to inflict maximum casualties.
Afghan soldiers and police are taking on responsibility for battling the militants from 100,000 NATO combat troops who will leave by the end of next year -- 13 years after a US-led invasion brought down the Taliban regime.
The Italian soldier was killed and three others were wounded when a grenade was thrown into their vehicle, local officials said.
"Today at around 10:30 am (local time), an enemy on a motorcycle threw a grenade on a convoy of Italian forces who were driving on a patrol in Farah city," Abdul Rahman Zhowandi, Farah provincial spokesman, told AFP.
The Italian defence ministry and military said the attack happened as the convoy was returning to base.
