France's military chief of staff said that French forces will be in direct combat with Islamist militants in Mali "within hours".
Admiral Edouard Guillaud said French ground operations began overnight in the West African former French colony where militants linked to al Qaida have gained territory since seizing control of the country's north earlier this year.
Some fear more Islamist gains would turn the region into a launching pad for terrorist attacks on the West.
The move reversed France's earlier insistence that it would provide only air and logistical support for a military intervention led by African troops.
"Now we're on the ground," Admiral Guillaud said. "We will be in direct combat within hours."