Russia launched checks Tuesday after its space chief said an air leak on the International Space Station last week could have been deliberate sabotage.
Space agency chief Dmitry Rogozin said the hole detected Thursday in a Russian space craft docked at the orbiting station was caused by a drill and could have been done 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.
"There were several attempts at drilling," Rogozin said late Monday in televised comments.
He added that 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 commission will seek to identify the culprit by name, Rogozin said, calling this a "matter of honour" for Russia's Energiya space manufacturing company that made the Soyuz.
Previously Rogozin had said the hole in the side of the Soyuz ship used to ferry astronauts was most likely caused from outside by a tiny meteorite.
"We have already ruled out the meteorite version," Rogozin said late Monday.
A Russian MP who is a former cosmonaut suggested that 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 ruled out -- it's really bad," said 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."
The hole is in a section of the Soyuz ship that will not be used to carry astronauts back to Earth.
A space industry source told TASS state news agency that the spacecraft could have been damaged during testing at Baikonur cosmodrome in Kazakhstan after passing initial checks and the mistake was 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.
Energiya will carry out checks for possible defects on all Soyuz ships and Progress unmanned ships used for cargo at its production site outside Moscow and at Baikonur cosmodrome, RIA Novosti reported Tuesday, citing a space industry source.
The ISS is one of the few areas of Russia-US cooperation that remains unaffected by the slump in relations between the countries and Washington's sanctions.
Russia's rockets used for launching spacecraft and satellites have suffered engine problems.
Currently on the ISS are two cosmonauts from Russia and three NASA astronauts as well as one German astronaut from the European Space Agency.