People attempting to reach Russia's Ministry of Construction, Housing and Utilities were welcomed with a "Glory to Ukraine" sign in Ukrainian.
Quoting, Russia's state news agency RIA late on Sunday, Reuters reported a ministry representative as saying that the site was down but users' personal data were protected.
According to RIA, hackers were demanding a ransom to prevent the public disclosure of users' data. Greek City Times was not able to ascertain which media outlets were being cited by the RIA.
Many Russian state-owned companies and news organisations have suffered sporadic hacking attempts since Russia sent its armed forces into Ukraine on February 24.
Hacking attacks in early May kept video-hosting site RuTube offline for three days and altered satellite television menus in Moscow on Victory Day, when Russia celebrated the 77th anniversary of the Soviet Union's victory over Nazi Germany.
Separately, Ukraine’s UNIAN news agency reported on Sunday that the broadcast of the Ukraine-Wales soccer match by OLL.TV online was temporarily hacked.
Moscow says it is carrying out a "special military operation" to disarm Ukraine and protect it from fascists. Ukraine and Western countries dismiss Russia's claims as a pretext to invade.