PARIS (AP) — France’s army chief of staff is dismissing an Islamic State group affiliate’s claim that it caused a helicopter collision in Mali that killed 13 soldiers.

Gen. Francois Lecointre on Friday told French radio RFI that no shots were fired at the helicopters. The Islamic State in the Greater Sahara has claimed responsibility but offered no evidence.

Lecointre said complex coordination during a combat operation was the cause of Monday night’s accident in the West African nation.

He said the helicopters’ flight data recorders will provide more details, saying the soldiers’ families are owed the truth about what happened.

It was France’s highest military death toll in nearly four decades.

The crash drew global attention to an emerging front for IS-linked groups as IS loses strength in Syria and Iraq.