Updated with Borisov's statement.
The launch of a Russian Soyuz MS-25 spacecraft to the International Space Station (ISS) was aborted just seconds before liftoff on Thursday, with officials blaming a loss of pressure at a power source.
"There was an automatic launch cancellation," a flight controller said in a live stream broadcast by Russia's space agency Roscosmos right before the rocket was set to take off from the Baikonur Cosmodrome in Kazakhstan.
On board the Soyuz rocket were Russian cosmonaut Oleg Novitsky, first-time spaceflight participant from Belarus Marina Vasilevskaya and NASA astronaut Tracy Dyson.
NASA said in a post on X (formerly Twitter) that "the spacecraft and crew remain safe. Teams at Baikonur will provide updates as they make assessments."
The head of Roscosmos Yury Borisov later explained that the mission abort was due to a loss of pressure at a power source.
The launch was rescheduled to 3:36 p.m. Moscow time on Saturday, he added.
Later on Thursday, SpaceX is scheduled to launch a robotic cargo mission to the ISS.
AFP contributed reporting.
