A malfunctioning gas generator in the Soyuz carrier rocket's third stage engine has been identified by members of the emergency commission as the reason a supply ship didn't make it to the International Space Station, Federal Space Agency (Roscosmos) spokesman Alexei Kuznetsov told the Itar-Tass on Monday.

It is a malfunction in the engine's gas generator, he said.

The unmanned Russian cargo ship Progress 44 malfunctioned shortly after its Aug. 24 launch, and the ship crashed in Siberia. It was supposed to carry 2.9 tons of supplies to the orbiting lab.

Russian space vehicles are the only means of transporting crews and supplies to the station now that the U.S. space shuttle program has ended. The U.S. space shuttle flew its last mission in July.

The space station is a joint project between the U.S., Russia, Canada, Europe and Japan, and it has been continuously staffed since November 2000.

It is believed that the astronauts on board the International Space Station may temporarily abandon the research facility this fall because of the failure of the unmanned cargo mission.

The Russian Federal Space Agency had established a commission to assess the root cause of the failure, to develop a plan of corrective action and to determine any implications for the launch of crews to the station on similar Soyuz rockets.

There are six astronauts currently on the space station and NASA officials have said they shouldn't be affected by the Progress crash because they have enough supplies to last a while on orbit.

Three of the astronauts are to return to Earth next month. The remaining crew is expected to return in mid-November, according to Space.com.

Itar-Tass has reported that in the meantime, more aircraft will be sent to the Progress spaceship fall area to look for debris. The paper also noted that Roscosmos has been conducting the search using only one Mi-8 helicopter belonging to the local Emergencies Ministry.

The number of aircraft will be increased, Alexander Puzanov, head of the Centre for Monitoring Carrier Rocket Debris Fallout Area in Siberia, told Itar-Tass. This will allow us to enlarge the search area. We will use all aircraft available in the region.

The search resumes on Tuesday, if the weather permits.

Puzanov said they couldn't take off on Monday because of poor weather conditions.