On Monday morning US mission commander Michael Foale discovered a crack in the US module that he and Russian flight engineer Alexander Kaleri sealed, the officials said.

The US section would be sealed off for at least 24 hours and the astronauts would transfer food, water and documentation from there to the Russian section, Pavel Vinogradov, the cosmonaut chief at the Energia corporation, told ITAR-TASS news agency.

"The crew will isolate the American Destiny module for a period of time on Wednesday from other sections of the craft to make sure that it is hermetic," he added.

Foale would move into the Russian part of the station while the US one remained sealed off, he said.

Monday's development followed a drop in cabin pressure aboard the ISS last week.

"The decay, which is currently measured at a rate of less that 0.04 pounds per square inch a day, is having no impact on station operations and the crew is in no danger," the US National Aeronautics and Space Administrationsaid in a brief statement.

The agency did not say when a drop in air pressure was first noticed but US television network NBC News cited a confidential internal NASA report as saying it came to the attention of mission control on December 29.

Foale, 46, and Kaleri, 47, arrived on the ISS aboard a Russian Soyuz spacecraft last October.

SPACE.WIRE