A new report claims that Russian scientists have discovered traces of marine life living on the exterior of the International Space Station (ISS).

Vladimir Solovyev, the official in charge of Russia’s ISS segment, told the news agency Itar-Tass that tiny plankton and microscopic organisms had been discovered on the spacecraft's exterior, describing the finds as “absolutely unique”.

However, the truthfulness of Solovyev's claim is unclear, with Nasa refusing to confirm the story. “As far as we're concerned, we haven't heard any official reports from our Roscosmos colleagues that they've found sea plankton," Nasa spokesperson Dan Huot told Space.com.

Huot confirmed that Russian cosmonauts had been taking samples from the windows on their side of the ISS, but clarified that they'd only been looking for “residues that can build up on the visually sensitive elements".

“I don't know where all the sea plankton talk is coming from,” Huot added.

Although the reports from Itar-Tass have not been confirmed, the idea of life existing in the harsh environment of space (surviving cosmic radiation, freezing temperatures and zero gravity) is quite possible.

A study in January 2013 found evidence of microbial life five to ten miles above the surface of the planet, while a type of microscopic invertebrate known as a tardigrade has even survived the vaccum of space for 10 days, shrugging radiation exposure a hundred times necessary to kill humans.