Preliminary findings indicate that the firing of the third stage of a Soyuz-2.1a launch vehicle that lifted off from the Baikonur space center on April 28 was the most likely cause of the off-nominal placement of a Progress M-27M cargo spacecraft into orbit, a source close to the commission investigating the incident told Interfax-AVN on Thursday.

"The incident affecting the third stage occurred five or six seconds before the cargo spacecraft's separation from it, after which telemetry transmission was stopped," the source said.

"Despite the loss of telemetry, the video surveillance channel remained in operation," he said.

"It made it possible to see that the spacecraft started spinning with a rotational velocity higher than the acceptable one by an order of magnitude, which immediately destroyed the Progress control system," the source said.

The source stressed that the findings were preliminary.

"The commission will present the final conclusions on the reasons behind the incident on May 13," he said.

A Soyuz-2.1a launch vehicle manufactured by the Samara-based Progress rocket and space center carrying the Progress M-27M spacecraft was launched from the Baikonur space center on April 28. After the spacecraft separated from the launch vehicle's third stage, it reached an unplanned orbit. According to the United States Space Surveillance Network, which is part of the U.S. Strategic Command (USSTRATCOM), about 20 fragments of the launch vehicle's third stage also appeared in outer space.

Any attempts to bring the spacecraft under control have been unsuccessful, it has started deorbit in an uncontrolled mode and may fall to Earth on May 8.