Morin's comments came after the Netherlands withdrew its troops from the country last weekend, Radio France Internationale reported.
"The French army had to stay in Afghanistan, because there is no other solution," Morin said. "If we were not in Afghanistan, Afghanistan would collapse again."
Morin said he hoped to begin withdrawing France's 4,000 troops and transferring "a certain number of zones to the Afghans" by early next year, RFI said.
The Dutch deployment in Afghanistan ended Sunday.