Three US service members have been killed and three others wounded in an explosion near Ghazni 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.
Taliban militants said they carried out the attack, their latest near the strategic city south of the capital.
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.
On 3 November, Utah mayor Brent Taylor was killed in an apparent insider attack while serving with the US Army National Guard to train Afghan security forces.
Earlier this month, Afghan President Ashraf Ghani said more than 28,000 Afghan police and soldiers had been killed since 2015.
For the past year, US and Afghan officials had withheld such information as it was deemed too sensitive, reported the New York Times.
In October, a local police chief was killed when a bodyguard opened fire on a group of US and Afghan officials in the southern Kandahar province.
US General Scott Miller escaped unhurt in that attack, which was later claimed by the Taliban.
A total of 13 US troops have been killed this year in Afghanistan, according to the Defense Post publication.
Why are US troops in Afghanistan?
American-led 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, which do most of the fighting.
The Taliban's power and reach has surged since then - and the number of security personnel being killed has soared.
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.