French troops have pressed northwards in Mali towards territory occupied for months by Islamist militants, military officials said, announcing the start of a land assault which will put soldiers in direct combat "within hours".
French ground operations began early on Wednesday in Mali, said Admiral Edouard Guillaud, the French military chief of staff.
France's defence minister said soldiers were heading away from the relative safety of the capital towards rebel strongholds in the north of the West African former French colony.
Five days of air strikes have done little to erode the Islamist gains, which some in the West fear could turn the region into a launching pad for terrorist attacks. The ground assault 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."
On Tuesday, France announced that it was increasing the number of troops from 800 to 2,500. The offensive was to have been led by thousands of African troops pledged by Mali's neighbours, but they have yet to arrive, making it increasingly apparent that France will be leading the attack rather than playing a supporting role.
A French military spokesman said on Tuesday that the Islamists had managed to seize more territory despite the air assault because the fighters were embedding themselves with the population, making it difficult to bomb without causing civilian casualties.
Admiral Guillaud said the militant groups had a history of taking human shields and France would do its utmost to make sure civilians were not wrongly targeted. "When in doubt, we will not fire," he said.
Supplies for the French forces arrived in a steady stream on Tuesday, part of the enormous logistics operation needed to support thousands of troops in the baking Sahara sun, a terrain the Islamists have operated in for nearly a decade.
On Tuesday, US Defence Secretary Leon Panetta reiterated the Obama administration's position, saying no American troops will be sent. The US is helping with communications and intelligence-gathering, and may allow American aircraft to help with transport.