Moscow, Aug 30 (IANS/RIA Novosti): Large pieces of the Russian Progress M-12M space freighter have not been found after it crashed in Siberia because the spaceship most likely burned up in the earth's atmosphere, an official said.

"Large pieces of the space freighter have not been found because they probably burned after an explosion of the third stage of the Soyuz-U carrier rocket. There had to be a lot of kerosene and liquid oxygen in the fuel tanks at the time of the emergency," a space industry source said Monday.

The Progress M-12M, carrying food and other items to the International Space Station, fell in South Siberia's Altai Republic Aug 24 after failing to separate from its carrier rocket.

This was the first loss of a Progress freighter in the history of Russia's space industry. A rocket engine failure caused the accident.

"On the other hand, the taiga (coniferous forest area) is large and the weather is awful, after the rain it began snowing, meaning it will be extremely difficult to find even small fragments of the Progress," the source said.

The freighter was carrying toxic heptyl fuel, although experts say it would have burned up in the atmosphere. Russian medical officials have said no trace of the fuel has been discovered.