MOSCOW, July 31 (Reuters) - The head of Russia's Roscosmos space agency said on Saturday that pressure in a Russian service module on the International Space Station had dropped as a result of an air leak.

Pressure had fallen over a two-week period before a Russian research module, the Nauka, threw the station out of control when its engines fired shortly after docking on Thursday, but Roscosmos head Dmitry Rogozin said the two events were not linked.

The fall in pressure was a result of a known minor air leak in an isolated transfer chamber of the Zvezda service module and pressure will be raised in the next 24 hours, Roscosmos said in a statement.