The pressure is diminishing at a rate of about 1 mm of mercury a day. According to a centre spokesman, there are no grounds for anxiety, since this is a "very insignificant figure".
If the situation continues to go on this way, oxygen supplies for adequate breathing will last the crew more than 180 days, believe Russian specialists.
Earlier in the week, the crew registered a pressure drop aboard the ISS of about 2,5 mm a day. That this indicator has now slowed to 1 mm "even offers grounds for moderate optimism," said the centre's spokesman.
So far neither Russian nor American mission controls are ready to pinpoint the cause of malfunctioning. In order to spot it, the cosmonauts aboard - Russia's Alexander Kalery and Michael Foale - are now investigating compartment after compartment by means of an ultrasound device.
Experts do not rule out that the pressure on board may even up without crew intervention. The Russian spokesman recalled that a similar phenomenon was observed aboard the Russian Mir station, but ceased by itself.