Russia began checks yesterday as its space chief said an air leak found on the International Space Station could be sabotage.
Space agency boss Dmitry Rogozin said the hole, found on Thursday in a Russian spacecraft docked at the orbiting station, was caused by a drill and could have been made deliberately, either back on Earth or by astronauts in space.
Astronauts used tape to seal the leak after it caused a small loss of pressure that was not life-threatening. Currently on the ISS are two cosmonauts from Russia, three NASA astronauts and a German from the European Space Agency.
"There were several attempts at drilling," Mr Rogozin said late Monday in televised comments, adding the drill appeared to have been held by a "wavering hand".
"What is this: a production defect or some premeditated actions?" he asked.
"We are checking the Earth version. But there is another version that we do not rule out: deliberate interference in space."
A state commission will seek to identify the culprit by name, Mr Rogozin said, calling this a "matter of honour" for Russia's RKK Energia space manufacturing company which made the Soyuz craft.
Asked about possible sabotage, a NASA spokeswoman referred all questions to the Russian space agency which is overseeing the commission's analysis.
Mr Rogozin had said the hole in the side of the ship used to ferry astronauts was most likely caused from outside by a tiny meteorite, but later admitted this had been ruled out.
A Russian MP and former cosmonaut suggested a psychologically disturbed astronaut could have done it to force an early return home.
"We're all human, and anyone might want to go home, but this method is really low," Maxim Surayev of President Vladimir Putin's ruling party, told RIA Novosti state news agency,
"If a cosmonaut pulled this strange stunt — and that can't be ruled out — it's really bad," said Mr Surayev, who spent two stints on the ISS.
"I wish to God that this is a production defect, although that's very sad, too — there's been nothing like this in the history of Soyuz ships."
Alexander Zheleznyakov, a former space industry engineer and author, told TASS state news agency that drilling the hole in zero gravity would be nearly impossible in that part of the spacecraft.
"Why would cosmonauts do it?" he asked.
The hole is in a section of the Soyuz ship that would not be used to carry astronauts back to Earth.
A space industry source told TASS the spacecraft could have been damaged during testing at Baikonur Cosmodrome in Kazakhstan after passing initial checks and the mistake then hastily covered up.
"Someone messed up and then got scared and sealed up the hole," the source speculated, but then the sealant "dried up and fell off" when the Soyuz reached the ISS.
Energia will check for possible defects on all Soyuz craft and Progress unmanned ships used for cargo at its production site outside Moscow and at Baikonur, RIA Novosti reported.
The ISS is one of the few areas of Russia-US cooperation that remains unaffected by the countries' tense relations and Washington's sanctions.