A space official said the sound might have been produced by equipment on the station, but a spokesman for Russia's Space Forces attributed the noise to a brush with floating space junk.

Valery Lyndin, a spokesman for Mission Control outside Moscow, said that ``all the station's systems are working normally'' after the sound was reported early Wednesday. An inspection of the station's outer surface by outside cameras found no sign of damage, he told The Associated Press.

Sergei Gorbunov, a spokesman for the Russian Aerospace Agency, said on NTV television that the crew heard what ``sounded as if a tin can was being crushed,'' but the ensuing check had found no trace of impact.

"The check made by the crew found no changes either in the equipment section or the atmosphere of the station, which would have changed instantly if the station's skin were punctured," Gorbunov said.

The station is manned by U.S. astronaut Michael Foale and Russian cosmonaut Alexander Kaleri.

Gorbunov said that the sound might have come from some of the station's equipment, not a collision.

However, a spokesman for the Russian Space Forces, which focus on monitoring the Russian satellite fleet but also keep track of the space station, said that the station had collided with a piece of space junk.

The spokesman, who spoke to the Associated Press on condition of anonymity, said by telephone that the space forces had detected an object along the station's orbit. They determined that the object was very small and would pose no danger to the craft.

Thousands of debris from spacecraft orbit around the Earth, and the Space Forces monitor them to make sure there is no threat to the station or satellites. In case a piece of debris is big enough to threaten damage, the spacecraft are directed to a safer orbit.