Several Russian government websites have been brought offline, including those of the Kremlin, State Duma, and Ministry of Defense.
Real-time network data shows "impact to FSO networks consistent with previous cyberattacks," Internet outage tracker NetBlocks tweeted on February 26.
The outages, which come as Russia invades Ukraine, follows after Ukrainian government websites were brought down by DDoS attacks.
It is not known who was behind this most recent attack against Russian websites, nor the previous one.
Members of the hacktivist collective Anonymous this week said that they would launch attacks against the Russian government.
Anonymous claimed credit for some outages, including of Russian news outlet RT, and said that it deface local government sites. It also claimed that it would leak login credentials for the Russian Ministry of Defense website.
Hours before the attacks began, Yegor Aushev, co-founder of a Kyiv-based cybersecurity company, told Reuters that he was asked by a senior Ukrainian Defense Ministry official to call on the hacking community for help with offensive and defensive.
This Saturday, the Minister for Digital Transformation of Ukraine Mykhaylo Fedorov, said: "We have many talented Ukrainians in tech: developers, cyber-specialists, designers, copywriters, marketing specialists, targeting specialists, etc.
"We are creating an IT Army."
The 'IT Army' posted a number of target sites to hack or bring down, including Sberbank, Gazprombank, Ministry of Defense, and Yandex.
On the other side of the conflict, ransomware groups Conti and CoomingProject said that they would support the Russian government.
"If anybody will decide to organize a cyberattack or any war activities against Russia, we are going to use our all possible resources to strike back at the critical infrastructures of an enemy," Conti said, in what is believed to be a response to articles claiming President Biden has been presented with options to launch cyberattacks against Russia.
"We do not ally with any government and we condemn the ongoing war," Conti said in a follow-up message. "However, since the West is known to wage its wars primarily by targeting civilians, we will use our resources in order to strike back if the well-being and safety of peaceful citizens will be at stake due to American cyber aggression."
Previous DDoS attacks of Ukraine have also been attributed to vigilante Russian hackers, per the BBC.