BAMAKO, Mali -- Mali's military claimed Friday that it has held control of a key town where Islamic extremists had battled forces for a week, though aid groups warned they were unable to reach the area to provide humanitarian assistance.

Meanwhile, the United Nations warned that some 700,000 civilians could be displaced by the fighting in Mali, where France launched a military intervention last week to oust the rebels from power in the north.

The French took action after the Islamist militants advanced from their stronghold in the vast, desert north toward the central Malian town of Konna.

A Malian military official, who spoke on condition of anonymity because he was not authorized to speak to journalists, said Friday that they were holding the town and that the Islamists had been chased out.

Telephone lines were cut off in the town, making it difficult to independently verify the claim.

Doctors Without Borders has been trying to get to Konna since Monday but all roads leading to the community in central Mali have been closed by the Malian military, said Malik Allaouna, director of operations for the group known as MSF by its initials in French.

"Despite our repeated requests, we are still being refused access to the Konna region," he said. "It is essential to allow the delivery of neutral and impartial medical and humanitarian aid in the areas affected by the conflict."

In Geneva, U.N. refugee agency spokeswoman Melissa Fleming said that the number of displaced Malians is expected to increase dramatically in the coming months.

Those who have fled "mentioned that large amounts of money are being offered to civilians to fight against the Malian army and its supporters," she said.

Meanwhile, forces remained on high alert in Banamba, a town just 90 miles (144 kilometers) from the Malian capital, Bamako, after a reported sighting of jihadists in the vicinity. Roughly 100 Malian soldiers sped Thursday to Banamba, which would be the closest the extremists have come to Bamako.

France has encountered fierce resistance from the extremist groups, whose tentacles extend not only over a territory the size of Afghanistan in Mali, but also another 600 miles (1,000 kilometers) to the northeast in Algeria, where fighters stormed a BP-operated plant and took dozens of foreigners hostages, including Americans.

They demanded the immediate end of the hostilities in Mali, with one commander, Oumar Ould Hamaha, saying that they are now "globalizing the conflict" in revenge for the military assault on Malian soil.

On Thursday, France increased its troop strength in Mali to 1,400, said French Defense Minister Jean-Yves Le Drian.

West African neighbors also have begun sending troops to aid the French-led mission, with Togolese forces arriving Thursday.

Nigeria has offered another 900 soldiers, while Chad has said it will send 2,000 to aid the mission.

A former French colony, Mali once enjoyed a reputation as one of West Africa's most stable democracies with the majority of its 15.8 million people practicing a moderate form of Islam. That changed last March, following a coup in the capital which created the disarray that allowed Islamist extremists to take over the main cities in the distant north.