The return of humans to the Moon, already postponed last week by NASA from 2024 to 2025, will actually take place in 2026 "at the earliest", according to a government audit published on Monday.

The Artemis program to return Americans to the Moon is encountering "technical difficulties and delays heightened by the Covid-19 pandemic and weather events," NASA's auditing body, the Office of Inspector General, said in a report.

"NASA's goal to land astronauts on the Moon's South Pole in late 2024 faces multiple significant challenges including major technical risks, an unrealistic development schedule, and lower-than requested funding levels," the report said.

First, the new space suits needed for the mission will not be ready "until May 2025 at the earliest," it said, noting "technical challenges and lack of funding.

Russia's space agency said on Tuesday its "main priority" was the safety of the International Space Station's crew, after the US accused Moscow of putting the astronauts under threat with a missile strike.

US officials on Monday denounced Russia for conducting a "dangerous and irresponsible" missile test that blew up one of its own satellites, creating a debris cloud that forced the ISS crew to take evasive action.

The move reignited concerns about a growing arms race in space, encompassing everything from laser weapons to satellites capable of shunting others out of orbit.

In its first comments following the US accusations, Russia's Roscosmos space agency did not deny there had been a missile strike.