"There are 12 crew members aboard the plane. All are the Air Force personnel. Five of them have been confirmed dead," Indonesian military (TNI) spokesman Major General Fuad Basya told Metro TV.
The fate of seven others was not known yet but the bodies of the fallen soldiers had been transported to Adam Malik Hospital for a postmortem examination, he said.
"But I cannot verify their personal identities," he said adding that the ill-fated transport plane, which crashed shortly after taking off from Polonia Air Force base was "fit for flying".
The transport plane with registration number A-1310 crashed shortly after taking off from Polonia airbase on its flight from Medan to Tanjung Pinang and Natuna Island in Riau Islands Province, the TV station reported.
The ill-fated aircraft carried supplies from Halim Perdanakusuma Air Force base in Jakarta to several air bases, such as Pekanbaru, Medan, Tanjung Pinang, Ranai (Natuna Island) and Pontianak.
The exact figure of casualties has yet to be known but the crash site is widely known as one of the busiest roads connecting Medan and Brastagi tourist resort.