France carried out multiple air strikes in Mali on Sunday as officials warned that the "spectacular acceleration" of al-Qaeda-linked fighters would have seen the capital fall to the rebels last week.
Jean-Yves Le Drian, the defence minister, said French and Malian forces had made progress towards stopping the rebel advance toward Bamako, the capital of the former French colony.
"There was a spectacular acceleration of these (jihadi) groups since Thursday. If no one intervened, Bamako would have fallen two or three days later," he said. "France is at war against terrorism."
France launched its first air strikes alongside the Malian army on Friday, in an attempt to push back advancing rebels, described by one Elysée source as "well equipped, well armed and well-trained".
Security controls in France were stepped up to reflect the heightened risk of a terrorist attack on French soil as one rebel commander said France had "opened the gates of hell".
Britain was preparing to send two military transport planes to Bamako, the capital, to help airlift supplies north towards the area of fighting.
The first C-17 was due to leave RAF Brize Norton late on Sunday to fly to France to collect equipment before continuing to Mali.
Mark Simmonds, a Foreign Office minister, hinted British troops would eventually be sent to Mali to train an army capable of holding off al-Qaeda.
He said: "We may well, through a European Union mechanism, provide training and support for the Malian army to give them strength to bring back the integrity of the Malian country in totality."
Downing Street said on Sunday that no British personnel would be deployed in a combat role.
French Mirage jets on Sunday destroyed a former Malian army base that had been taken over by the al-Qaeda-allied militants who had used it as a major logistical headquarters.
The site, at Lere, is 100 miles into Islamist-held territory north of the loose border between militant and government land.
The jets carried out a series of low fly-bys on Sunday morning, dropping bombs that "completely razed" the facility, eye-witnesses and local officials said. Hundreds of the town's residents were fleeing.
The mission was part of a third day of strikes by France, which now has more than 550 air and ground troops in the West African country.
Elsewhere, storage hangars, weapons dumps and rebel vehicles were destroyed, according to the French defence ministry. Sunday's operations appeared to be focused on Islamist strongholds deeper inside the area it controls.
Attack helicopters were also reported to have launched strikes on militant positions in the city of Gao, one of the main centres occupied since the extremists took control of northern Mali following a coup last March.
"There are permanent raids. There are some at this moment, there were some last night, there will be more tomorrow," said Mr Le Drian.
At least 12 people have died since the start of the international action on Friday, including a French helicopter pilot and three children who drowned when they ran into a river to escape an aerial bombing raid.
The offensive was authorised after Ansar Dine, the main rebel group, which is linked to al-Qaeda, took the town of Konna on Thursday and promised to push on south into government-held territory.
Up to 500 troops from Mali's neighbours, Niger, Burkina Faso and Senegal, and Nigeria, the regional power, have been pledged to the operation.
French soldiers were already patrolling Bamako where the state television station broadcast footage of troops moving in single file through the streets. They are there to protect major sites from militant attack, the French said.
It is not clear how long Francois Hollande will keep his country's troops in Mali.
Dominque de Villepin, a former prime minister who led the French opposition to war in Iraq in 2003, led criticism of French involvement.
"War is not France," wrote Mr de Villepin in a newspaper column. "Let us not give into the reflex of war for war's sake," arguing that wars in Afghanistan, Iraq and Libya never stopped terrorism in those regions, and simply made matters worse.
"We're fighting blindly, for lack of a goal," he wrote. "How has the neoconservative virus won over everyone's thinking?"