Monday's failed satellite launch was caused by a fault in a fuel pipe, Kommersant daily reported on Thursday, citing a source in the government inquiry.
The source said telemetry showed that pressure in the Briz-M upper stage fell sharply following the vehicle's second burn, causing the Proton-M rocket, carrying two communications satellites, to spin out of control.
The launch was scheduled to utilize four burns of the Briz-M to put Indonesia's Telkom-3 and Russia's Express MD2 satellites into orbit.
The Briz-M's fuel pipe might have been "mechanically damaged" or held some foreign objects, the inquiry source said.
The failed launch has prompted Russian space agency Roscosmos to suspend all Proton-M launches until the findings of the inquiry are returned.
Roscosmos declined to comment on the cause of the failure when contacted by RIA Novosti.
Last year, a malfunction of a Briz-M booster led to the loss of the Express-AM4 telecommunication satellite.