The Sunday deaths brought the number of NATO troop deaths in Afghanistan to eight in the past three days, CNN reported.
Three other NATO servicemen died during so-called "green on blue" attacks, in which Afghan forces turn their guns on NATO troops, ISAF said.
The other three deaths included one serviceman dying in an insurgent attack, one killed by a roadside bomb and one who died of non-combat related injuries, officials said.
Meanwhile, a senior former member of Afghanistan's Taliban Muslim extremist movement was assassinated in his car Sunday in Kabul, police said.
Arsala Rahmani was on his way to work at his senate office when a car pulled alongside and a gunman fired a single shot, the BBC said.
"Mr. Rahmani was shot in his heart and died instantly," Kabul Police Chief Ayub Salangi told the broadcaster. "His nephew, who was also his driver, didn't even realize he had been shot."
Rahmani was a member of the Afghan senate representing the eastern province of Paktika. He was also a member of President Hamid Karzai's peace council, founded to open dialogue with the Taliban, whose regime was toppled in 2001.
During the group's time in power, Rahmani was the minister for higher education, the Khaama Press reported.
There was no immediate claim of responsibility for the attack, the reports said.