PARIS (AP) ― A French soldier was shot to death on Tuesday in a clash with jihadists in a mountainous region of Mali’s far north, a critical operation in France’s bid to end a growing stranglehold by radicals who had imposed an extreme brand of Islam over more than half the West African country and threatened the borders beyond.

The death of the French Legionnaire, announced by President Francois Hollande, brings to two the number of French troops who have been killed since France launched a surprise military intervention in its former colony on Jan. 11 to push out militants who had taken over the country’s vast north. A helicopter pilot was killed on the first day of the intervention.

The latest death also marks the darkest side of the operation as special forces moved into the rocky terrain of the Adrar des Ifoghas mountain range, thought to be the region where seven French hostages are hidden ― and where jihadists chased from cities they once controlled are thought to have taken refuge.

Military spokesman Col. Thierry Burkhard said 20 extremists were killed on Tuesday.

He said French armored vehicles and Mirage jet fighters hit enemy positions. Air strikes also destroyed two munitions depots.

Hollande vowed to keep up the fighting until “the last chiefs of the terror groups” are eliminated, and said the operation is in its “last phase.”

“At this moment we have special forces who are in the north of Mali and who are intervening in a zone that is particularly delicate, which is the Ifoghas mountain range, where terror groups are holed up,” he said during a visit to Greece.

“There was a serious clash with several deaths on the side of the terrorists, but also a death on the French side,” Hollande said, adding that the soldier killed came from a Legionnaire parachute regiment.

The French-led operation is aimed at preventing the extremists, who are inspired by radical Islam, from taking over all of Mali and destabilizing the region. In justifying the surprise French intervention, Hollande often said that Europe and France were threatened by a takeover of Mali by radicals. Among the leading terror groups is an al-Qaida offshoot, the Algeria-based al-Qaida in the Islamic Maghreb.

France has been joined by African troops and is to hand over the military intervention to them with Malian forces in the lead. However, no date has been set. The latest operation was launched on Monday by nearly 150 French and Malian soldiers.

French parachute commandos opened Tuesday’s action shortly before 11 a.m., backed by an armored patrol on a reconnaissance mission, a Defense Ministry statement said. They headed into the Adrar des Ifoughas region, 50 kilometers south of the town of Tessalit which is not far from the Algerian border.

The French forces received support from the armored patrol, which opened fire with 105mm cannons, the military said. Burkhard said the Legionnaire died of gunfire in a clash that lasted five to six hours and involved two French Mirage fighters and a quick-reaction force.

French and Malian forces quickly took back the northern cities of Timbuktu and Gao, but for weeks have been unable to retake the city of Kidal farther north. Insurgents have made forays into Gao since the French arrived.

The move into the Ifoghas region, further north, has been the toughest part of the operation. Families of the seven hostages thought to be held there fear their loved ones may be killed in reprisal for the intervention.

Hollande said the French action was aimed at cutting the head off the jihadist groups. He said French forces have liberated cities, but still must arrest “the last chiefs of the terror groups that remain in the extreme north of Mali.”

Hollande said there is “no risk of stalemate” in Mali.

Mali was plunged into turmoil after a coup in March 2012 created a security vacuum that allowed secular rebel Tuaregs to take half the north as a new homeland. In the following months, the rebels were kicked out by the extremists adhering to a radical interpretation of Islam and who imposed strict Shariah law.

The campaign has heightened concerns for Westerners’ safety around western Africa.

On Tuesday, a group of French tourists _ four children and three adults -- was kidnapped in Cameroon and reportedly taken to neighboring Nigeria, where extremist Islamist groups have seized other foreign hostages, French officials said. That brings to 15 the number of French hostages in west Africa.