His Malian counterpart Dioncounda Traore has sought help from France, the country's former colonial power, to stem the rebels' advance.
Until now, France -- like other EU nations -- has limited its plans for assistance to training and logistics support for Mali's troubled army.
But in a speech Friday to France's diplomatic corps, Hollande went a step further, saying he was ready to respond to Mali's call for help.
France "will be ready to stop the terrorists' advance if it continues," he said. He did not spell out what help it would offer.
He said the rebels were destabilizing the entire region and calling into question the existence of Mali itself. He said France would seek United Nations resolutions for any action.
Extremists who have controlled the north for months captured the city of Konna on Thursday and are threatening the city of Mopti -- with 100,000 inhabitants. The capture of Mopti would leave the capital Bamako more vulnerable.