According to a statement from Russia's Interior Ministry, Russian police claim it found propaganda on the dark web for a terrorist attack order against Moscow.
The mysterious dark web includes a number of dark web sites that can only be accessed with authorization through specific software, thus ensuring the anonymity of users.
The Interior Ministry said, "In the course of monitoring the Internet, employees of Russia's Interior Ministry detected a number of propaganda messages calling for terrorist activities in the shadow part of the Internet - the Dark Web, the Hydra website, as well as social networks and instant messengers."
The Interior Ministry added: "According to the available information, the announcements calling for illegal acts were made by call centers located in Ukraine. Police said that previously these centers may have engaged in telephone fraud and other criminal acts against Russian citizens."
In materials posted online, the attackers offered rewards for carrying out terrorist attacks, including against Russian state authorities.
Russia's Interior Ministry has asked "citizens not to respond to provocative offers posted on the Internet."
Local police say that "participation in terrorist activities, hooliganism and other violations should be subject to criminal liability."
With the proliferation of disinformation and the amplification of military claims and counter-claims on social media, determining exactly what is happening is difficult.
As Russian and Ukrainian websites have fallen victim to cyber attacks and Moscow has restricted access to some foreign social media, Internet users in both countries have turned to other online tools such as the dark web and VPN to help circumvent these blockades.
Demand for virtual private networks (VPN) that encrypt data and hide the IP addresses where users are located soared, peaking at 354 percent in Russia on Sunday compared with the daily average from Feb. 16 to 23.
Calling its military operation in Ukraine a "special operation," Russia invaded its neighbor on Feb. 24, launching attacks from land, sea and air. Inside Russia, it is struggling to control rhetoric, threatening to impose restrictions on foreign and local media that deviate from its official version of the story.
Photos and videos are slow to load on both Facebook and Twitter, sites owned by Meta, both of which have been targeted by Russia's state communications regulator Roskomnadzor.
"Demand for VPN in Russia has surged as authorities restricted Facebook and Twitter over the weekend to control the flow of information from their incursions into Ukraine."
Russia banned several VPN last year, but failed to stop them entirely because critics say they stifle Internet freedom.
In Ukraine, Russian hackers were accused of launching a string of cyber attacks that briefly shut down Ukrainian banks and government websites in the days before the invasion. Russia denies this.
Demand for VPN in Ukraine also began to increase significantly on Feb. 15 in light of the cyberattacks and spiked after the invasion, with demand 424 percent higher than the daily average for the first half of February.
On Monday, several Russian media outlets had their websites hacked and their regular sites replaced with anti-war messages and calls to stop President Vladimir Putin's intrusion.