"In response to the request from the Malian authorities, Defence Minister Jean-Yves Le Drian decided to send a unit of French special forces," the ministry said, adding they had come in from Burkina Faso.
The units were "in place from 2:00 pm French time (1300 GMT)", the ministry said.
US special forces are also involved in the operation at the Radisson Blu hotel and have rescued at least six Americans, a US military spokesman said.
