Malian, French and U.N. forces have launched an offensive in northern Mali to prevent any resurgence of activity by Islamist militants in the region.

Malian and French military officials announced the joint operation on Thursday, a day after two Chadian soldiers were killed by suspected militants at a checkpoint in the northern town of Tessalit.

The French news agency says about 1,500 troops are involved in the operation, including 600 French and 600 Malian soldiers. It was not immediately clear when the operation began.

In January, France led an offensive to drive al-Qaida-linked militants out of Mali's northern cities. Subsequently, however, some of the militants moved to more remote regions of the country.

The Chadian soldiers killed Wednesday were part of a U.N. peacekeeping mission that is taking over security responsibilities in the region.

Mali has seen an increase in unrest in recent weeks.

Earlier this month, President Ibrahim Boubacar Keita cut short a trip to France after fighting erupted between Malian soldiers and MNLA rebels in Kidal. He also returned to respond to a mutiny at a military camp near Bamako.

Mr. Keita's government has been trying to restore order after 21 months of turmoil that included an ethnic Tuareg uprising, a coup in Bamako and an Islamist militant takeover of the country's north.