Russia says it will withdraw from the International Space Station (ISS) after 2024 and build its own station instead.
The US and Russia, along with other partners, have successfully worked together on the ISS since 1998.
But relations have soured since Russia invaded Ukraine, and Russia previously threatened to quit the project because of Western sanctions against it.
Nasa said it had not yet received any official notice of Russia’s intention to withdraw from the program.
The ISS – a joint project involving five space agencies – has been in orbit around Earth since 1998 and has been used to conduct thousands of scientific experiments.
It is approved to operate until 2024, but the US wants to extend that for six more years with the agreement of all partners.
At a meeting with Russia’s President Vladimir Putin, Mr Borisov said Roskosmos would fulfill its obligations to its partners, but the decision had been taken to quit the project after 2024.
“I think that by this time we will start putting together a Russian orbital station,” Mr Borisov said, adding that the new station was his agency’s top priority.
“Good,” replied Mr Putin.
It is not immediately clear what the decision means for the future of the ISS, and the US space agency Nasa says it has not received any formal notice from Russia of its plans.
Former ISS commander and retired US astronaut Dr Leroy Chiao believes it is unlikely Russia will decide to leave the project.
The Russians have been making noises about withdrawal for some time but it’s not clear how serious they are.
They’ve talked about building their own outpost – the Russian Orbital Service Station – but it would require a financial commitment the Russian government has not shown to the country’s existing space exploits.
Certainly, Russian elements on the ISS are aging but the view of engineers is that the modules can do a job through to 2030.