The monitoring centre for Russia's public communications network said on Tuesday its specialists had recorded a "massive failure" of Telegram although it was not immediately clear why.
Telegram did not reply to a request for comment.
"The work of Telegram messenger and a number of other services in Russia is already being restored," Russia's digital ministry said in a statement, adding that there had also been failures of the app outside Russia.
"We are working to establish the cause of the incident," it said.
"As for Russian telecom operators, their networks are operating normally."
Reuters correspondents in Moscow noted outages of Telegram, YouTube and Vkontakte for about 90 minutes.
Soon after the outage, several previously blocked social media apps including Instagram and Facebook suddenly became available in Russia on Tuesday, according to Reuters reporters in Moscow.
Reuters reporters were able to browse Instagram without requiring a virtual private network (VPN) for the first time since blocks were imposed shortly after Russia sent tens of thousands of troops into Ukraine in February 2022.
Communications regulator Roskomnadzor has moved to block some foreign tech companies including Meta Platforms' Facebook and Instagram.
Russia has long sought to improve its domestic internet infrastructure, or Runet, even disconnecting itself from the global internet for tests.
Anton Gorelkin, deputy head of the State Duma parliamentary committee on information policy, said it was unclear what had caused the Telegram outages but that immediately blaming the Russian state was a mistake, noting "conspiracy theories" that Russia was trying to block foreign resources prior to a March presidential election.
"There have been, and will be, such incidents for a variety of reasons: from human error to hacker attack," he said.
"Much more important is how long it takes to eliminate the failure; the scale of damage to the Russian economy depends on this."
