MOSCOW -- Two Russian cosmonauts at the International Space Station (ISS) started on Monday a spacewalk, which was delayed by nearly an hour due to minor problems with airtightness, the Mission Control Center said.

According to the schedule, Russian cosmonauts Gennady Padalka and Yury Malenchenko should open the station's hatches at 6:40 p.m. Moscow time (1440 GMT), but the mission was delayed to 7:38 pm Moscow time (1538 GMT).

"A leak occurred in an airlock chamber between the station's Pirs and Zvezda modules," the center told reporters.

The spacewalk was to last for some six and a half hours. Padalka and Malenchenko will perform several maintenance works, including moving a mechanical arm from Pirs module to Zarya module, launching a research microsatellite "Sphere" and conducting other works as assigned.

Other four ISS crew members remained inside the station.

This was Padalka's ninth spacewalk and Malenchenko's fifth one. It was also the first spacewalk of the 32nd Expedition of the ISS.

The spacewalk coincided with the deorbiting of Russia's Progress M-15M cargo ship, which started at 7:20 pm Moscow time (1520 GMT).

The freighter, undocked from the ISS on July 31, will be " buried" in the Southern Pacific at about 1600 GMT.