An official involved in Russia's participation in the International Space Station is claiming sea plankton and other microorganisms have been found clinging to the station's external surfaces.

Media reports have quoted Vladimir Solovyov as saying cosmonauts aboard the orbiting laboratory have discovered miniscule amounts of organisms on instruments on the station's exterior despite their being exposed to the harsh vacuum of space.

"Results of the experiment are absolutely unique. We have found traces of sea plankton and microscopic particles on the illuminator surface. This should be studied further," Solovyov, head of the the Russian ISS orbital mission, said.

NASA, for its part, says it has not been informed of any such finding by Roscosmos, Russia's equivalent to the U.S. space agency.

"As far as we're concerned, we haven't heard any official reports from our Roscosmos colleagues that they've found sea plankton," NASA spokesman Dan Huot said.

Russian media has said the findings came from long-term studies involving specialized equipment operated by Russian crew members on the space station.

Previous studies have shown microorganisms are able survive in outer space amid harsh conditions including vacuum, extreme temperatures and cosmic radiation.

A number of American and European space missions have demonstrated microbes can survive for extended periods of time in low Earth orbit, NASA scientists say.

Still, they say, they remain skeptical of the Russian claims of sea plankton, noting that their experiments were not meant to be looking for microbes.

Instead, they were taking samples from a window on the Russian portion of the ISS looking for residues building up on its surface from periodic thruster firing meant to refine the space station's orbit.

"That's what they were taking samples for," Huot said. "I don't know where all the sea plankton talk is coming from."

NASA does monitor its spacecraft, including the ISS, for bacteria that might be growing inside that could pose a risk to astronauts, says Cynthia Collins, who led one such study for the space agency.

"Before we start sending astronauts to Mars or embarking on other long-term spaceflight missions, we need to be as certain as possible that we have eliminated or significantly reduced the risk that biofilms pose to the human crew and their equipment," she says.

It's possible that the plankton, if it is indeed confirmed, may have gone into space on the Russian module when it was launched, NASA said.