PARIS (AP) — Islamic State group-linked fighters claimed responsibility Thursday for a helicopter collision that killed 13 French soldiers earlier this week in Mali, while France said it will reassess its military operation in West and Central Africa after its deadliest toll in nearly four decades.

The Islamic State in the Greater Sahara statement came almost three days after the low-flying helicopters collided on a moonless night while pursuing extremists near the border with Niger. An investigation has begun into the cause of the crash.

French President Emmanuel Macron told reporters that “our mission there is important, yet what we are now living in the Sahel leads us to look into all strategic options.”

He said the French government and armed forces will work on the issue in the coming weeks.

Macron this week defended France’s largest overseas military mission, which involves 4,500 troops, saying it is aimed at enhancing France’s own security and providing support to African countries.

A national tribute ceremony will take place Monday in Paris.

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Associated Press writer Baba Ahmed in Bamako, Mali contributed.