As Russian forces moved into Kyiv, Moscow's defence ministry also said that Russian media should stick to the official version of events.

In a statement, the communications watchdog accused a number of independent media outlets of spreading "unreliable socially significant untrue information" about the shelling of Ukrainian cities by the Russian army and civilian deaths.

These included television channel Dozhd and the country's top independent newspaper Novaya Gazeta, whose editor Dmitry Muratov was awarded the Nobel Peace Prize last year.

On Thursday, Russian leader Vladimir Putin unleashed a full-scale invasion of Ukraine that according to Kyiv has already killed 198 people including three children and sparked fears of a greater conflict in Europe.

Citing a request from the General Prosecutor's Office, the Russian communications regulator said the media outlets -- that also include Echo of Moscow radio -- will be blocked unless they remove the "unreliable information".

"Roskomnadzor also launched an administrative investigation into the dissemination of unreliable publicly significant information by the above-mentioned media," the watchdog said.

The offence is punishable by a fine of up to five million rubles ($60,000), it said.

Roskomnadzor also said that "reliable information" could be found in "official Russian information outlets".

- 'Stoned gang of nationalists' -

The Russian defence ministry followed suit, calling on the media "to be vigilant and not become blind victims of Western curators (leading) information pressure on our country".

The ministry singled out Novaya Gazeta, accusing it of spreading "fake information prepared by a stoned gang of (Ukrainian) nationalists".

Its statement echoed Putin, who called Kyiv's leadership a "gang of drug addicts and neo-Nazis" on Friday.

Novaya Gazeta published its Friday issue in Russian and Ukrainian in solidarity with Ukraine.

"We will never recognise Ukraine as an enemy and the Ukrainian language as the enemy's language," its editor Muratov said in a video.

Moscow has not yet provided any details of Russian losses in the fighting in the face of statements from Kyiv that they have inflicted heavy casualties on Moscow's forces.

The invasion of Ukraine is taking place during an unprecedented crackdown on the Russian opposition, with top protest leaders assassinated, jailed or forced out of the country.