Thirteen French soldiers were killed when their two helicopters slammed into each other during an anti-terrorism combat operation in Mali, marking the single biggest loss of life in years for France’s army.

The collision took place in low altitude during a mission to support ground forces battling terrorist groups late on Monday, according to the French ministry of defense.

All soldiers on board died, the presidency said in a separate statement. President Emmanuel Macron saluted their “courage.”

The deaths bring to more than 30 the number of French soldiers killed in Mali since 2013 when France’s military intervened to stop a loose alliance of ethnic Tuareg separatists and Islamist fighters that had seized the north from moving south toward the capital, Bamako.

More than 4,500 French troops -- a force known as Barkhane -- have since been deployed to fight Islamist militants and hunt down their commanders in the western Sahel - an arid band on the southern fringe of the Sahara desert that stretches through some of Africa’s poorest and least-governed states. Still, violence by al-Qaeda and Islamic State militants is increasing, with more than 100 Malian troops killed this month in a spate of attacks on remote border posts.

Among the raids was a Nov. 18 attack that killed 24 Malian soldiers. The same day, during a visit to Senegal, French Prime Minister Edouard Philippe said the regional military operation would maintain its pressure on terrorist groups.

“I would like to extend my condolences to the families and friends of the 13 French soldiers,” government spokesman Yaya Sangare said by phone from the capital, Bamako, on Tuesday. “France and its military operation Barkhane have been crucial for the fight against terrorists in Mali and to re-establish the sovereignty of Mali’s territory.”

French and Malian troops have intensified their operations in a region known as Menaka over the past few weeks, he said, in an attempt to track and target terrorists at their bases. The tragic accident came after two large-scale attacks against Malian army garrisons in this particular region, Sangare said.

The biggest loss in a French oversees military operation was the 1983 attack against soldiers stations in Lebanon when a bomb hit the building called Drakkar, killing 58. (Agency report)

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