Astronauts relocate after space station alarm

The U.S. astronauts are safe, the agency said.

The Russian Federal Space Agency earlier reported that there was a leak in the cooling system, but NASA described the relocation as a precautionary move following an alarm. A leak has not been confirmed, NASA said.

The American section of the space station is isolated while astronauts investigate the cause of the alarm.

NASA said its crew responded to increased pressures in the station's cooling loop. This could indicate an ammonia leak, NASA said.

Two U.S. astronauts are aboard the International Space Station -- commander Barry Wilmore and flight engineer Terry Virts.

"So, big-picture perspective, we're trying to figure out exactly what happened. We're not entirely convinced that this is an ammonia leak," Wilmore told NASA Mission Control in Houston.

It is possible that the alarm was set off by a faulty sensor or some other cause, he said.

They joined Samantha Cristoforetti, a flight engineer with the European Space Agency, and others in the space station's six-member crew.

"Hey everybody, thanks for your concern," Cristoforetti tweeted. "We're all safe & doing well in the Russian segment."