Technicians at work on the BRIZ-M upper stage.
Photo is courtesy of Krunichev.

...was caused by a fuel line fault, with this information coming to that publication via a source involved in the government inquiry of the incident. The source stated telemetry showed that pressure in the Briz-M upper stage fell off 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 use four burns of the Briz-M to place 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.