Astronauts onboard the International Space Station have been ordered to shelter in their spacecraft and prepare for potential evacuation as a Russian crew attempts to fix a worsening leak of air in its portion of the orbital laboratory, Nasa has said.

The four astronauts of Nasa’s Crew-12 mission on the station – two US astronauts, a French astronaut and a Russian cosmonaut – received orders from Nasa mission control at 9.04am ET (2pm BST) on Friday to enter their Crew Dragon spacecraft docked to the station and don their spacesuits in case the air leak warranted an emergency evacuation, a Nasa official said.

Nasa and Russia’s space agency Roscosmos, the station’s two primary operators, have debated for months over the cause and potential fixes of small air leaks onboard Russia’s Zvezda service module, a key structure of the football-pitch-sized laboratory.

The air leaks have been relatively minor in recent months. But on Monday the problem escalated from a pound of air per day to two pounds (0.9kg) a senior Nasa official told Reuters on condition of anonymity.

More details soon …