Following an operation that uncovered more than 800 instances of violent or terrorism-related content, Europe's policing agency issued a warning on Monday that the threat posed by transnational right-wing extremist communities online is growing.

Recent shootings in Slovakia and the United States "show a worrying development of violent right-wing extremist and terrorist operations on a global scale," according to Europol.

"The perpetrators of these attacks were part of transnational online communities and took inspiration from other violent right-wing extremists and terrorists," it added in a statement.

Last Thursday, police from 13 member states of the European Union and from the United Kingdom participated in a "referral action day" to flag extremist and violent right-wing material online, such as livestream broadcasts, manifestos, and claims and celebrations of attacks.

The Hague-based body said in a statement that police subsequently forwarded the content to online service providers, and their responses to the referrals were assessed.

"The activities resulted in the referral of 831 items to 34 affected platforms," Europol said, stressing that “the threat posed by violent extremism and terrorism is still on the rise."

Two assaults that were attributed to violent right-wing extremism and may have been influenced by online content were highlighted by Europol.

The first was the self-declared white supremacist Payton Gendron's murder of 10 Black individuals in Buffalo, New York, in the United States, in May of this year.

The second incident took place when a "radicalized teenager", believed to be the son of a prominent member of a far-right party, shot dead two men outside a bar in Slovakia's capital Bratislava in October.

According to Europol, these acts have brought to light the crucial role that online propaganda played in their radicalization process.

"This shows how the abuse of the internet continues to be an important aspect of violent right-wing radicalization and recruitment," it added.

After the arrest of 25 suspected coup plotters in Germany earlier this month, when prosecutors claimed they were preparing to remove the government and install their own, another recent instance of escalating right-wing violence in Europe occurred.

At the time, anti-terrorist experts argued that the group was influenced by online conspiracy theories, such as the QAnon hypothesis, and was "seriously convinced" that a "deep state" was in charge of running Germany and needed to be overthrown.

Read more: 2021 Roundup: The rise of the radical right