Three US service members have been killed and three others wounded in a bomb explosion near Ghazni city in Afghanistan.
A US civilian contractor was also hurt by the improvised explosive device, the Nato-led mission said in a statement.
Officials would not give further detail until next of kin were notified, saying only that the injured were evacuated and receiving medical treatment.
This is the second attack in a month targeting US forces in the region.
Utah mayor Bret Taylor was killed in an apparent insider attack on 3 November while serving with the US Army National Guard to train Afghan security forces.
On Saturday, a US soldier was killed in Nimroz province in what appeared to be an accidental shooting, the Nato-led mission also announced on Tuesday.
A total of 13 US troops have been killed this year in Afghanistan, according to the Defence Post.
Last month, US Gen Scott Miller escaped unhurt when a bodyguard opened fire on a group of US and Afghan officials in the southern Kandahar province.
The local police chief was killed in that attack, which was later claimed by the Taliban.
Why are US troops in Afghanistan?
American combat operations against the Taliban officially ended in 2014, but some US troops remain in the country to provide training and assistance to Afghan forces.
Last year, US President Donald Trump signalled he would keep US boots on the ground indefinitely amid concerns that the Taliban was gaining ground.
The US forces are part of the Nato-led Resolute Support Mission in Afghanistan, which has more than 16,000 personnel.
Source BBC News