A Russian cosmonaut who explored a mysterious hole in a capsule docked to the International Space Station has said the opening was drilled from inside the spacecraft.

Sergei Prokopyev said investigators are looking at samples he and crewmate Oleg Kononenko collected during a December 12 spacewalk as Russian law enforcement agencies examine what caused it.

Mr Prokopyev and two other astronauts returned to Earth last week from a 197-day space station mission.

The hole in the Russian Soyuz spacecraft attached to the station was spotted on August 30.

The crew discovered a leak that was creating a slight loss of pressure and plugged the hole with epoxy and gauze.

Russian cosmonaut Sergey Prokopyev
Sergei Prokopyev (Dmitri Lovetsky/Pool/AP)

Mr Prokopyev said at a news conference that the cavity started from the capsule’s interior and “it’s up to the investigative organs to judge when that hole was made”.

The astronauts’ quick identification and repair of the hole demonstrated “the crew was ready for any developments”, he said.

The hole did not pose a danger to Mr Prokopyev and crewmates Serena Aunon-Chancellor, of Nasa, and Alexander Gerst, of the European Space Agency, during their return because the section of the capsule it appeared on was jettisoned before the fiery re-entry into Earth’s atmosphere.

Roscosmos chief Dmitry Rogozin said in September the hole could have been drilled when the capsule was manufactured or in orbit.

Mr Rogozin stopped short of blaming crew members, but the statement has caused some friction between Roscosmos and Nasa.

He has since back-pedalled from the statement, blaming the news media for twisting his words.

Mr Prokopyev scoffed at the idea the hole could have been drilled by an astronaut, saying: “You shouldn’t think so badly of our crew.”