There are fears of a third wave of coronavirus in Moscow, after the Russian capital recorded more than 9,000 new infections.
Kremlin spokesman Dmitry Peskov said President Vladimir Putin was monitoring the situation closely.
"Total nihilism, the low vaccination level was behind the surge. We also shouldn't forget the cunning of the infection itself."
The city's mayor further extended restrictions he had imposed this month.
They include a ban on public events with more than 1,000 people, an 11 p.m. closing time for cafes and restaurants, and the closure of fan zones set up for the European soccer championship.
Moscow's new infections made up more than half those reported across the country.
Authorities this week ordered all workers with public-facing roles in Moscow to have a vaccination.
And on Friday, the city government said only vaccinated residents would be able to receive non-emergency treatment in hospitals.
As of June 2nd, the most recent tally available, only 18 million Russians had received at least one dose of vaccine so far: at just one-eighth of the population, it's far less that most Western countries.
Back in April, Reuters reported that several Russian officials and members of the business elite had already been securing third and fourth doses of Sputnik V.
The question of how long a vaccine offers protection against COVID-19 for will be vital as countries gauge when or whether revaccination will be needed.
Russia's findings will be closely watched.