A woman wearing an Afghan security forces uniform on Monday killed a contractor working for the NATO-led International Security Assistance Force (ISAF) in Kabul, according to Reuters.
There are conflicting reports, but a NATO spokesman told the news service that a U.S. police adviser was killed.
An ISAF statement said only that a “contracted civilian employee” was killed at Kabul's police headquarters.
It appeared to be the first time that a female member of Afghanistan's security forces carried out such an attack, Reuters said.
At least 53 troops have been killed this year due to insider attacks, according various reports, most of them American.
In addition to undermining the trust between Afghan police and the coalition forces charged with training them, the incidents raise doubts about the ability of NATO to successfully transition control of security to Afghan forces by the end of 2014.
Some fear a civil war or an outside attack could threaten the country, with Taliban or other insurgent groups looking to take advantage of the struggling young Afghanistan army when coalition forces withdraw.
Pentagon officials have called the insider attacks a last-ditch infiltration effort by the Taliban, and argue that some of the attacks are due to personal disputes.
Still, it’s the latest troubling news to come out of the unpopular war.
U.S. Navy SEAL commander Job Price died Sunday in Afghanistan, although the Department of Defense has classified it as a “non-combat fatality.” An anonymous U.S. official told CNN and NBC the death was a suspected suicide.
Earlier this month, gunmen killed a female government official in a drive-by shooting, a police chief was killed by a roadside bomb, and an intelligence chief was wounded in a bombing assassination attempt, among others.
—This report was originally published at 6:20 a.m. and last updated at 10:18 a.m.