The Lockheed C-130 Hercules was one of two ex-US Air Force planes delivered to the Philippines this year as part of military aid. General Cirilito Sobejana, the Chief of Staff of Sulu province, said the plane crashed soon before noon Sunday in Bangkal hamlet, near the hilly town of Patikul.

According to Sobejana, the jet was transporting troops from southern Cagayan de Oro city. For decades, government forces have fought Abu Sayyaf insurgents in the largely Muslim region of Sulu. The cause of the collision was not immediately known.

“It’s very unfortunate,” Sobejana told reporters. “The plane missed the runway and it was trying to regain power but failed and crashed.” Sobejana stated at least 40 people on board were brought to a hospital while troops were trying to save the rest.