ACM Sutthipong Inseeyong, director of the Air Operation Control Directorate who headed the search mission, said the two pilots and a mechanic for the helicopter were all killed.
The UH-1H Huey lost contact over the Khao Chamao-Khao Wong National Park that straddles Rayong and Chanthaburi provinces. The chopper was en route to provide supplies to an Air Force radar station.
Sutthipong said the helicopter was found on a 1,000-metre-high mountain. The spot was only 500 metres from the Air Force rador station and was about two kilometres away from the Rong Thao Naree Mountain.
Parts of the helicopter were scattered over the area.
A source said the bodies of the three might be retrieved during the day.
The two pilots were identified as Sqn Ldr Pasit Techasen and Flight Lt Alongkorn Chankrajang. The mechanic was identified as Flight Sgt 1s Class Wisut Puttharaksa.
The helicopter was found after the Army on Monday reinforced both aircraft and the search team.
Army chief General Theerachai Nakvanich ordered the dispatch of a Blackhawk and Mi-17 helicopters, as well as three 14-member operation teams to search for the missing chopper.