MOSCOW, February 12 (RIA Novosti) - The debris from a collision involving two communications satellites poses no threat to the International Space Station (ISS), a spokesman for Russia's space agency (Roscosmos) said on Thursday.

Alexander Vorobyov said that while Roscosmos could not confirm the origin of the satellites the risk to the ISS and its crew of three was minimal.

"There are no registered losses in the Roscosmos satellite grouping," Vorobyov added.

NASA said earlier that one of 66 satellites privately owned by Iridium, a U.S. telecoms company, and a Russian satellite launched in 1993 and believed to be defunct collided on Tuesday "in the first-ever crash of two intact spacecraft in orbit."

According to NASA, the collision occurred nearly 500 miles (805 kilometers) over Siberia and a "flash" would have been visible in the night sky.

"This was the worst such incident that has ever occurred," Nicholas Johnson of NASA's Johnson Space Center said.

Each satellite weighed well over 455 kilograms (1,000 lbs).

Space collisions are rare events and normally involve parts of spent rockets or mini-satellites.

"It will be weeks at least before the true magnitude of these clouds are known," NASA also said. "The risk to the space station is considered to be very small and within acceptable limits."

Analysts expect the wreckage from the collision to burn up in the Earth's atmosphere.