It was "very likely" that the two Dutch soldiers, aged 20 and 22, were killed by fire from their compatriots, and an investigation had been launched to find out what happened, he said.
In the same area on Saturday, Dutch troops killed two allied Afghan soldiers when the Afghans, who were not in army uniforms, approached and acted strangely, the spokesman said.
The Dutch soldiers were also under fire and were treating a colleague whose legs later had to be amputated, the spokesman said.
Separately, four Canadian soldiers were wounded on Sunday when a landmine exploded during a mine removal operation on a road near Kandahar in southern Afghanistan, Canadian media cited military officials as saying.
None of the soldiers were seriously hurt.