A Su-25 Frogfoot close-support aircraft exploded in the air on March 20 during a live firing exercise over the Primorye Territory about 143 kilometers (90 miles) from the port of Vladivostok. The pilot died in the crash.
"The investigation conducted by a special commission established that the Su-25 strike aircraft was downed by a missile accidentally launched by a wingman," the source said.
It had previously been suggested that the crash was caused by the explosion of an S-8 rocket during its launch from the doomed plane.
However, a Russian Air Force spokesman warned on Wednesday against jumping to any conclusions until the official investigation was complete.
"The investigation is still under way," Colonel Alexander Drobyshevsky said.
"An official announcement regarding the cause [of the crash] can only be made by the head of the special investigation commission after the investigation is complete," he said.
The Air Force suspended all Su-25 strike aircraft flights following the incident and until the investigation is complete, although a small group of Su-25s will take part in a parade on Moscow's Red Square on VE Day, May 9.
The Su-25 is a single-seat, twin-engine jet aircraft developed by the Sukhoi Design Bureau to provide close air support for ground troops.
The aircraft is reported to have experienced a number of accidents in operational service caused by system failures attributed to the salvo firing of weapons.
The Su-25 aircraft has been in service with the Russian Air Force for more than 25 years. In 1999, Russia adopted a program to upgrade part of its aging Su-25 fleet. The Russian Air Force received the first six modernized planes, Su-25SM, in December 2006.