Islamist militants gained ground in one Malian town on Monday even as government troops stepped up their offensive to wrest control from rebels.
Militants have taken control of the central town of Diabaly, French Defense Minister Jean-Yves Le Drian said, according to CNN affiliate BFM TV.
Word of the rebel advance on Monday came as the U.N. Security Council met to discuss the conflict in Mali, where Islamist rebels have been seizing territory for months.
World leaders from a number of countries have said they'll send troops or provide logistical support for the fight against Islamist militants in the West African nation.
France took the international lead in assisting Mali over the weekend, with military airstrikes targeting rebel training camps and other targets.
Officials said France's intervention last week was necessary to stop a rebel takeover of the capital, Bamako.
"Our assessment was that they (the rebels) were actually able to take Bamako. So we decided that what was at stake was the existence of the state of Mali, and beyond Mali was the stability of all west Africa," said Gerard Araud, French ambassador to the United Nations. "We had no other choice to launch this military intervention."
The United States has promised to help the French effort, U.S. Defense Secretary Leon Panetta said Monday. That assistance could include logistical and intelligence support.
"I commend France for taking the steps that it has. And what we have promised them is that we will work with them to cooperate with them and to provide whatever assistance we can to try to help them in that effort," Panetta told reporters on his plane en route to Portugal.
The United States has already started sharing intelligence from satellites and intercepted signals with the French, defense officials said on Monday.
In addition, the Pentagon is considering sending refueling tankers so that French jets can fly longer, more sustained combat missions, according to the officials.
Drones "are under consideration," the defense officials said, though the military's stash of unmanned aerial vehicles is in heavy demand.
Both stressed that these would be surveillance drones and said there are no plans yet to deploy them.
U.S. State Department spokeswoman Victoria Nuland, meanwhile, said the United States is reviewing a number of requests from the French, but that no decisions have been made.
The United States, she said, is "not in the position to support the Malian military directly until we have democratic processes restored by way of an election in Mali."
It was unclear Monday when France's role in the military offensive would end, and whether there could be consequences beyond Mali's borders.
"There are risks in France and in other countries as well," Le Drian told BFM. "We are extremely vigilant in that regard."
Malian Foreign Minister Tieman Hubert Coulibaly said Monday that it was unclear how long clashes with Islamist militants would last.
"Clearly, for us it's not just about making them retreat," he told BFM. "It is necessary to chase them out."
Coulibaly said his country was grateful for France's assistance, which it "urgently requested." And Mali may call on other countries such as the United States for military aid, he said.
"It is a problem which is currently in Mali, but which concerns the whole civilized world. And those who are in action against Mali could attack the rest of the world," he told BFM. "It is a cancer which could have spread if we had not intervened, of course, with the precious aid of France."
France has several hundred ground troops in Mali, and nearby West African nations have pledged to send hundreds of troops to join in the fight. Nigeria, which already has a technical team on the ground in Mali, expects to have troops in the country by next week, a presidential spokesman told CNN. He declined to say how many soldiers would be deployed.
Officials from the United Kingdom and Germany have said they're considering offering logistical support to the Malian government as it fights insurgents controlling the north.
As French fighter jets bombed rebel strongholds over the weekend, both sides of the fight said they were determined to win.
"France's goal is to lead a relentless struggle against terrorist groups, preventing any new offensive of these groups to the south of Mali," France's Defense Ministry said in a statement.