PARIS — French soldiers in Mali have begun a major anti-insurgent sweep with Malian forces and United Nations peacekeepers, the Defense Ministry said on Thursday, calling it the largest operation to counteract a revival of Islamist militant activity since France intervened early this year.

Col. Gilles Jaron, a French military spokesman, said the operation, named Hydra, had long been planned and was intended to thwart “a resurgence of terrorist movements.” He did not specify precisely when the operation had begun.

The large number of French troops now actively fighting the insurgents in Mali has raised questions about whether France, the former colonial power, would be able to reduce the number of soldiers there from 3,000 to 1,200 by the end of the year as planned.