The coalition said in a statement it was investigating the circumstances of the crash but gave no other information. The nationalities of those killed were not released, citing its policy that home countries should identify their casualties.
The deaths bring to seven the number of international troops killed in Afghanistan this month. The NATO force is preparing to withdraw its troops from Afghanistan at the end of this year, and it has already turned over the job of fighting the Taliban insurgency to the Afghan army and police.
Violence has increased in Afghanistan ahead of the NATO withdrawal and also in the weeks leading up to the country's April 5 election. Preliminary results of the vote are due later Saturday.
Also Saturday, an Afghan university official identified the two Americans killed in a shooting at a Kabul hospital earlier this week.
The vice chancellor of Kabul University, Mohammad Hadi Hadayati, named the two as health clinic administrator Jon Gabel and his visiting father, Gary.
Hadayati said that Jon Gabel's wife was wounded in the attack Thursday saw that an Afghan police security guard open fire as the family entered the grounds of Cure International Hospital.
The Gabel family was visiting pediatrician Dr. Jerry Umanos of Chicago, who was also killed in the shooting.
Hadayati said Jon Gabel ran a clinic at the university providing low-cost medicine and also volunteered to teach computer classes.
He said Gabel worked with U.S. charity Morning Star Development.