A small air leak has been detected on the Russian side of the International Space Station, thought to have been caused by a small meteorite.
Astronauts are continuing to try and plug the leak but NASA and Russian officials have stressed the six astronauts are not in any danger.
The leak, which was detected on Wednesday night, may be the result of a micrometeorite strike, according to the Russian officials.
"Overnight and in the morning there was an abnormal situation – a pressure drop, an oxygen leak at the station," said Roscosmos chief Dmitry Rogozin.
"A micro fracture was found, most likely it is damage from the outside. The design engineers believe it is the result of a micrometeorite."
It was found in the most recent Soyuz capsule, which is one of two docked at the space station and is home to three Americans, two Russians and a German.
Mr Rogozin said the leak would be patched up from the inside.
NASA confirmed the problem and said it consisted of a "minute pressure leak", which crew members were repairing. On Twitter, it confirmed "all systems are stable" despite the "tiny leak".
Space officials said the leak had been "isolated to a hole about two millimetres in diameter" and slowed through the use of thermoresistant tape, but added that a more permanent solution was being developed.
In a statement, NASA added: "The leak, which was detected Wednesday night by flight controllers as the Expedition 56 crew slept, resulted in a small loss of cabin pressure.
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"Flight controllers determined there was no immediate danger to the crew overnight."
The capsule arrived at the orbiting lab in June with three astronauts and it is due to take them home in December.