"Three Resolute Support service members were killed by a suicide bomber during a combined, dismounted patrol with Afghan forces in eastern Afghanistan," it said in a statement.
A US member of the patrol and two Afghan soldiers were wounded, it said, without giving the nationality of those killed.
The attack by a lone bomber on foot happened at 6am in the city of Charikar in Parwan province some 60 kilometres north of Kabul, said provincial governor's spokesman Wahida Shahkar.The Taliban in a statement claimed responsibility.
The US-led Nato force ended its combat mission in Afghanistan in 2014 and pulled out the bulk of its troops. A 16,000-strong residual force remains for training and counter-terrorism operations.
Last month a US soldier was killed and two others wounded in an "apparent insider attack" in southern Afghanistan, Nato said.A suicide bomber has killed three NATO service members on a foot patrol in eastern Afghanistan with Taliban militants claiming responsibility.
A NATO Resolute Support mission service member, an American, and two Afghan soldiers were wounded, the mission said in a statement."Their sacrifice will endure in both our hearts and history and further strengthen our resolve," said US Army General John Nicholson, commander of Resolute Support and US Forces-Afghanistan, in the statement.
Local officials said Sunday's blast happened in the Khalazai area of Charikar, capital of Parwan province.Wahida Shahkar, spokeswoman for the Parwan provincial governor, said the suicide bomber targeted foreign forces who were on a routine foot patrol.
Eastern Afghanistan, where US Special Forces units have regularly been deployed against militants, continues to be one of the deadliest areas for the US military since its main combat operation against the Taliban ended in 2014.
The Taliban, fighting to restore strict Islamic law after their 2001 ouster, claimed responsibility.
"We have killed eight US invaders in a tactic bombing," Zabihullah Mujahid, the Taliban spokesman, said in a statement."The invaders had to bring three helicopter ambulances to protect their forces," he said.
