France's armed forces began military intervention in Mali to help the government stem a push south by Islamist rebels who control much of the north, President Francois Hollande said.
"French forces brought their support this afternoon to Malian army units to fight against terrorist elements," President Hollande told reporters. "This operation will last as long as is necessary."
Mr Hollande said United Nations Security Council resolutions meant France was acting in accordance with international laws.
Earlier, Mr Hollande had made it clear that France would intervene to stop any further drive southward by Islamist rebels.
Malian soldiers launched a counter-offensive to wrest back a town captured by militants this week.
Western powers fear the alliance of militants that seized the northern two-thirds of Mali in April will seek to use the vast desert zone as a launch pad for international attacks.
Mali's government appealed for urgent military aid from France on yesterday, as interim president Dioncounda Traore declared a state of emergency.
Islamist fighters encroached further south, seizing the town of Konna in the centre of the country.
The rebel advance caused panic among residents in the nearby towns of Mopti and Sevare, home to a military base and airport.
The UNSC in December authorised the deployment of an African-led force supported by European states.