Taiwan authorities are investigating to determine why two military jets crashed into a mountain, killing three men.

Search crews pored over the site of the crash Wednesday, searching for clues to the cause and the remains of the flyers. The official Central News Agency reported that only partial remains had been found.

Officials said the RF-5 surveillance plane and two-seater F-5F trainer jet took off on a night training flight late Tuesday and disappeared from radar screens 13 minutes later.

Local fishermen reported seeing the planes flying erratically and crashing into a mountainside near the coast of northeastern Yilan county, creating a ball of fire.

Taiwan is hoping to replace its fleet of aging F-5 fighters with advanced F-16C/Ds if the United States agrees to sell it the planes. China has signaled its strong opposition to the sale. A decision is due next month.