One NATO soldier was killed by a friendly fire and several were wounded on Monday during a major offensive to crush a resurgent Taliban in southern Afghanistan.
The troops were strafed by two of their own warplanes after calling in air support during a battle at close quarters with Taliban fighters in Kandahar province, the alliance said in a statement.
And a British soldier died in a suicide bombing in Kabul, along with at least four civilians, including an Afghan working for foreign troops.
The bomber rammed his car into a NATO convoy on the highway between Kabul and the eastern city of Jalalabad, Interior Ministry spokesman Yousuf Stanizai said.
NATO launched Operation Medusa on Saturday, its biggest thrust against the Taliban since taking over in southern Afghanistan on July 31 in the largest ground operation in its history.
Monday's NATO fatality in Kandahar was its fifth combat death in the operation.
Four Canadians were killed over the weekend.
Another 14 British troops died when their plane crashed on Saturday in the early stages of the operation. NATO says the crash was due to technical problems, not enemy fire.
"Now, let me be very clear that (NATO) forces will continue their mission, deeply saddened by this loss but totally unaffected in their determination to build on the existing progress of Operation Medusa and finish the job," NATO chief Lieutenant-General David Richards said in a statement.
"Our comrades would expect no less."
In the recent months, Taliban forces have virtually retaken Kandahar, bordering Pakistan, leaving NATO barely in control of the provincial capital, Kandahar city.
NATO says it has killed more than 200 guerrillas in Operation Medusa. Afghan officials put the rebel toll in the dozens.
Fighting across Afghanistan is the worst it has been since US-led forces ousted the hardline Islamist Taliban in 2001.
More than 2,000 people, most of them militants, along with scores of civilians and aid workers and hundreds of Afghan security personnel, have been killed so far this year. More than 115 foreign troops have died.