It also comes as the Islamists advance ever closer toward the most northern city still under government control and after they fought the Malian military for the first time in months.
French President Francois Hollande said Friday that the operation would last "as long as necessary" and said it was aimed notably at protecting the 6,000 French citizens in Mali. Kidnappers currently hold seven French hostages in the country.
"French army forces supported Malian units this afternoon to fight against terrorist elements," he said.
The foreign minister, Laurent Fabius, said, "To the question of whether there was an aerial intervention, the response is yes." He wouldn't comment on troops on the ground, arguing that such information would give "hints to terrorists." He said France had discussed the move with U.S. officials earlier Friday.
France's announcement comes after residents in central Mali said they had seen Western military personnel arriving in the area, and that planes had landed at a nearby airport throughout the night.
Col. Abdrahmane Baby, a military operations adviser for the foreign affairs ministry, also confirmed in the Malian capital of Bamako that French troops had arrived in the country. He gave no details about how many were there or what they specifically were doing.
"They are here to assist the Malian army," he told reporters in the capital of Bamako.
France has led a diplomatic push for international action in northern Mali but efforts to get an African-led force together, or to train the weak Malian army, have dragged.
The French quickly mobilized after the Islamists seized a key town on Thursday, pushing closer to the army's major base in central Mali.
The United Nations Security Council has condemned the capture of Konna and called on U.N. member states to provide assistance to Mali "in order to reduce the threat posed by terrorist organizations and associated groups."
France's position has been complicated because for months, Hollande has said France would not send ground forces into Mali.
The French foreign minister insisted that the recent advances by the extremists made intervention necessary, and said the aim of the operation is to "stop the advance of criminal and terrorists groups on the south" of Mali.
Late last year, the 15 nations in West Africa, including Mali, agreed on a proposal for the military to take back the north, and sought backing from the United Nations.
The U.N. Security Council authorized the intervention but imposed certain conditions. Those include the training of Mali's military, which has been accused of serious human rights abuses since a military coup last year sent the nation into disarray.
The fighting Wednesday and Thursday over the town of Konna represents the first clashes between Malian government forces and the Islamists in nearly a year, since the militants seized the northern cities of Gao, Kidal and Timbuktu.
The Islamists seized the town of Douentza four months ago after brief standoff with a local militia, but pushed no further until clashes broke out late Wednesday in Konna, a city of 50,000 people, where fearful residents cowered inside their homes. Konna is just 45 miles north of the government-held town of Mopti, a strategic port city along the Niger River.
"We have chased the army out of the town of Konna, which we have occupied since 11 a.m.," declared Sanda Abou Mohamed, a spokesman for the Ansar Dine militant group, speaking by telephone from Timbuktu.
A soldier, who spoke on condition of anonymity because he was not authorized to speak to journalists, acknowledged that the army had retreated from Konna. He said several soldiers were killed and wounded, though he did not have precise casualty figures. "We didn't have time to count them," he said.
While Konna is not a large town, it has strategic value as "the last big thing ... on the road to Mopti," said J. Peter Pham, director of the Africa program at the Washington-based Atlantic Council.
"I think the real target here is to seize the airstrip in Mopti, either to hold it or blow enough holes in it to render it useless," Pham said. "If you can seize the airstrip at Mopti, the Malian military's and African militaries' ability to fly reconnaissance in the north is essentially clipped."
Al-Qaida's affiliate in Africa has been a shadowy presence for years in the forests and deserts of Mali, a country hobbled by poverty and a relentless cycle of hunger. Most Malians adhere to a moderate form of Islam, where women do not wear burqas and few practice the strict form of the religion.
In recent months, however, the terror syndicate and its allies have taken advantage of political instability to push into Mali's northern towns, taking over an enormous territory they are using to stock weapons, train forces and prepare for jihad.
The Islamists insist they want to impose Shariah only in northern Mali, though there long have been fears they could push further south. Bamako, the capital, is 435 miles from Islamist-held territory.