A gunman in an Afghan army uniform has opened fire on a group of US soldiers, killing at least two Americans, including a civilian, in Afghanistan's capital, Kabul.
The shooting took place at 11am local time (06:30 GMT) on Wednesday while international troops visited a military base in Kabul, according to Dawlat Waziri, a spokesman for the Afghan Ministry of Defence.
NATO said in a statement later on Wednesday that "one US service member and one US civilian died as a result of wounds sustained in Kabul".
The shooter was killed after an exchange of fire in the Rishkhor neighbourhood of Kabul, which houses an Afghan special forces training centre, according to NATO and Waziri.
The Americans were conducting duties as part of their mission to train, advise and assist Afghan forces when they came under attack, NATO said, adding that an investigation had been launched into the incident.
"Any time we lose a member of our team, it is deeply painful," said General John Nicholson, the top US and NATO commander in Afghanistan.
"Our sympathies go out to the families, loved ones, and the units of those involved in this incident. To those who continue to target coalition forces ... [we] will continue to pursue our mission to help our partners create a better Afghanistan."
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An American official said the shootout occurred at a military ammunition supply point near Camp Morehead, a base used for Afghan commando training.
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.
Dozens of international soldiers and advisers have been killed in attacks by Afghan security forces on their allies.
Since 2008, the blog Long War Journal has registered 92 such attacks with at least 150 international soldiers killed and 187 wounded.
Such attacks are sometimes caused by cultural misunderstandings or personal clashes.
Taliban fighters have also often managed to infiltrate the ranks of Afghan security forces to carry out so-called insider attacks in the past few months.
Source: News Agencies