The state news agency said the power cut may also delay the planned November 19 return to Earth of three ISS members who are completing their six-month mission on board the floating international space lab.
"We have not had a connection with the ground telemetry stationed in Russia for the past two hours," RIA Novosti quoted an unidentified source in the Russian space industry as saying.
"Our specialists lack the ability to control the civilian satellites or send commands to the Russian segment of the ISS," said the source.
"They can see the crew and can talk to them, but they cannot send any commands to the Russian segments."
The director of a Moscow region institute in charge of satellite and ISS communication told the Interfax news agency that the power cut appeared to have been caused by basic road repair work.
The unnamed industry source added that military satellites were not affected by the power cut and that the line would take at least 48 hours to fix.
"What happened is in no way related to the work being done by our specialists with the air and space defence forces," the source told RIA Novosti.
"Communications with the military satellites continue as always," the source said.