Nasa avoided questions about safety but said the astronauts were "doing great".

The US space agency said in a press conference on Wednesday that it will make a call by the end of August.

Officials also said that the astronauts’ space suits are unsuitable to wear on the alternative spacecraft that could be used if Starliner is deemed unsafe.

Nasa also said the two astronauts were “doing great” and went to space prepared for a risky mission.

Suni Williams and Butch Wilmor travelled to the International Space Station (ISS) on 5 June, expecting to return after eight days.