PARIS -- The French Defense Ministry said on Monday that a town in central Mali had fallen to Islamist insurgents from the north, hours after Foreign Minister Laurent Fabius said his country's dramatic intervention there had succeeded in blocking a rebel advance that could have had "appalling consequences."
At the same time, an Islamist leader in Mali said France had "opened the gates of hell" for all its citizens by intervening, reinforcing concerns that the far-flung military operation in Africa could inspire vengeance in mainland France.
French forces, Mr. Fabius said in a radio interview late Sunday, were now "taking care" of rear bases used by Islamists who took control of much of the north of the country last year after a military coup in the capital, Bamako. The duration of the French operation was "a question of weeks," Mr. Fabius said, unlike the American-led military campaign in Afghanistan.
But within hours, reports began to emerge of a rebel counterattack in the small town of Diabaly, north of Ségou on the approaches to the capital -- the first indication that the insurgents had regrouped after a wave of French airstrikes. The fighting in the town pitted government forces against rebels seeking to press southward under heavy fire from the air.
Reuters quoted residents and Malian military officials as saying that Islamists counterattacked after the insurgents infiltrated overnight in small groups. The French defense minister, Jean-Yves Le Drian, said the rebels "took Diabaly after fierce fighting and resistance from the Malian Army that couldn't hold them back."
The French intervention, which began on Friday and continued over the weekend, appeared to halt the main thrust of an Islamist rebel advance farther east, as West African nations authorized what they said would be a faster deployment of troops in support of the weak government.
French aircraft dropped bombs and fired rockets from helicopter gunships and jet fighters after the Islamists, who already control the north of Mali, pressed southward and overran the village of Konna, which had been the de facto line of government control.
The French struck two columns of Islamist fighters, the French Defense Ministry said. The first was in and around Konna, driving out the rebels from the village, and the second was to the west, across the Niger River, heading south toward Ségou.
That second column appeared from local accounts to still be advancing, with the rebels taking the small town of Alatona as well as Diabaly, a military camp on a main road to Ségou, the administrative capital of central Mali, according to The Associated Press.
A spokesman for the Malian Army, Lt. Col. Diarran Kone, confirmed the rebel attack on Diabaly.
The French defense minister, Mr. Le Drian, said on Monday that the situation in Mali "is evolving favorably," but he acknowledged that fighting continued.
"There is still a difficult spot in the west, where we're dealing with extremely well-armed groups and where the operations are ongoing," he said.
The rebel takeover of northern Mali began after the fall of Col. Muammar el-Qaddafi in Libya in October 2011, when Tuareg fighters from northern Mali, who had been fighting alongside Colonel Qaddafi's forces, returned home with weapons from Libyan arsenals.
They joined with Qaeda-affiliated Islamist militants who had moved to the lightly policed region from Algeria, and the two groups easily drove out the weakened Malian Army in late March and early April last year. The Islamists then turned on the Tuaregs, routing them and consolidating control in the region in May and June.
The rebels struck a defiant posture on Monday.
Oumar Ould Hamaha, an insurgent leader, said the French intervention had "opened the gates of hell for all the French."
He taunted French forces to open a ground offensive, saying French warplanes had bombed from high altitude. "Let them come down onto the ground, if they are men," he said. "We will greet them with open arms."
France, he told Europe 1 radio, "has fallen into a trap which is much more dangerous than Iraq, Afghanistan or Somalia. And that is only the beginning." On Sunday evening, French jets attacked the northern town of Gao, an insurgent stronghold.
Abdheramane Oumarou, a local counselor in Gao reached late Sunday after a day of French airstrikes, said: "We are in the best of all possible worlds. The planes have been circling Gao since 5 this morning. All of the sites they targeted, they hit. The airport. The warehouses, they destroyed them. These were all sites occupied by the Islamists, and they have been totally destroyed."
"The Islamists are in hiding. There were many dead," he said. For the first time since the insurgents overran the town last year, "the population of Gao will sleep soundly, and will even snore."
Despite concerns that support for France could provoke terrorist reprisals on its soil, Britain announced late on Saturday that it would help to transport foreign troops and equipment to Mali, though would not send its own soldiers to fight. Two British military transport planes were expected to head for Mali on Monday with equipment including French armored vehicles from a base in Normandy, the British Defense Ministry said.
"There is a very dangerous Islamist regime allied to Al Qaeda in control of the north of that country," Prime Minister David Cameron said on Monday. "It was threatening the south of that country, and we should support the action that the French have taken."
"So we were first out of the blocks, as it were, to say to the French, 'We'll help you, we'll work with you and we'll share what intelligence we have with you and try to help you with what you are doing,' " Mr. Cameron told the BBC in a radio interview.
Mr. Fabius, the foreign minister, said the military effort had three goals: to "block the advance of the terrorists, which is done"; to restore Mali's territorial integrity, "which will take more time"; and to secure the carrying out of United Nations Security Council resolutions on the Mali crisis. France has called for a meeting of the Security Council on Monday to discuss the situation in Mali.
"If France had not intervened," Mr. Fabius said, the rebels "could have reached Bamako, with appalling consequences" not only for the Malian population but also for the 6,000 French and other Western citizens living in the capital of the former French colony.
Mr. Le Drian, the defense minister, said Sunday that the rebels could have reached Bamako in "three or four days" if France had not intervened.
France now has more than 400 troops in Bamako, mainly to ensure the safety of French citizens and to send a signal to the Islamists, out of a total of 550 troops in Mali. The others, including some special forces, are in the town of Mopti in the south. It has also deployed Rafale jet fighters to attack rebel positions.
A French analyst, who is briefed on the situation but declined to be identified by name, said France believed the United States would deliver on promises of in-flight refueling for the air campaign, logistical support and reconnaissance.
The analyst said the dilemma facing French forces was now whether to maintain a United Nations schedule for West African and Malian troops to seek to recapture the north in the fall after seasonal rains, "which given the current dynamic seems hard to imagine," or to "speed things up and try to clear the north in the next eight weeks" before the rainy season.
That could extend the duration of the French intervention, the analyst said.
Steven Erlanger reported from Paris, Alan Cowell from London, and Adam Nossiter from Bamako, Mali.
This article originally appeared in The New York Times.