ISAF does not comment on the nationality of its casualties before their home nations have done so.
The force has also decided not to announce the province where casualties occur because this could suggest their nationality, a spokesman said.
Troops in southern Afghanistan include British soldiers in Helmand, Canadians in Kandahar and Dutch in Uruzgan. There are also deployments from Australia, Denmark, the US and other countries.
There are more than 33,000 ISAF soldiers in Afghanistan, about a third of them in the south, which is the heartland of the Taliban movement and sees most anti-government violence.
Also on Saturday, a US army general said a top Afghan anti-government leader operating from inside Pakistan sent some 200 ill-equipped fighters, some wearing plastic bags on their feet, into Afghanistan where most were killed in a major battle this week.
Benjamin Freakley said Jalaluddin Haqqani recruited and sent unemployed and untrained men to fight in Afghanistan.
US forces killed about 130 fighters moving in two groups in the eastern province of Paktika early on Thursday, one of the largest winter battles in Afghanistan since the fall of the Taliban in 2001.
"There's Taliban leaders in Pakistan," Freakley said. "We know that these groups ... were from Jalaluddin Haqqani and we believe, though we don't know exactly where, that Jalaluddin Haqqani is operating from inside Pakistan and sending men to fight in Afghanistan.
"It is clear to me that some of these men were just either collected in a poor part of a village or perhaps from a madrassa or perhaps from a refugee camp and told to come fight."
Freakley said it was likely the fighters meant to attack a new military outpost near the village of Marghah that has affected fighters' infiltration routes.
A Taliban leader has said in an interview broadcast by Al Jazeera on Saturday that his group would protect and guard al-Qaeda leaders Osama bin Laden and Ayman al-Zawahiri if they turned up in tribal areas bordering Afghanistan.
Mullah Mohammed Nazir, an official in charge of what are called Taliban Pakistani fighters in the tribal districts close to the border with Afghanistan, said: "I have not met Osama or al-Zawahiri and they did not come to our region. We hope to see them and if they show up in our area, we will protect them with our bodies and souls."
He denied that he had met bin Laden or al-Zawahiri, but said: "Pakistan has a religious and ethical responsibility to support the Afghan people to liberate their country."