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Russia's space agency says it is considering sending an empty spacecraft to the International Space Station (ISS) to bring home three crew members ahead of schedule, after their Soyuz capsule started leaking.

Roscosmos and Nasa said it was unclear how the external radiator on the spacecraft sustained a tiny puncture.

They have ruled out the impact of a meteor.

The leak started as two cosmonauts were preparing for a routine spacewalk.

A decision is yet to be made about how exactly the three crew members will be brought back to Earth.

The most likely option is to send another Soyuz spacecraft to collect them.

A less likely option is sending them home in the leaky capsule without most of its coolant, which regulates temperatures inside the crew compartment of the spacecraft.

The vehicle - known as MS-22 - flew Russian cosmonauts Dmitry Petelin and Sergey Prokopyev, as well as Nasa astronaut Frank Rubio, to the station in September.

But it began spraying coolant into space earlier this month, with Nasa TV capturing dramatic images of white particles streaming out of the capsule like snowflakes.

Joel Montalbano, Nasa's ISS program manager, said late February would be the most likely time to launch another Soyuz. The crew were due to return in March.

Nasa says that none of the crew are in danger.

The capsule is currently being vented with air flow allowed through an open hatch to the space station, Mr Montalbano said.

The ISS was launched in 1998 and is located about 400 km from the Earth.

Cosmonauts carry out tests and research at the station that will help future space missions.