Security experts have named "lone jihadi" attacks the biggest terror threat during the 2018 World Cup in Russia this summer.
Sunni Islamist militants, particularly Russian jihadists returning from conflict zones, are the primary source of concern for Moscow, according to a report released Tuesday by Jane's, the defense and security wing of IHS Markit.
The threat has been driven by Russia's military involvement in Syria and separatist militancy in its disputed Northern Caucasus region.
The Islamic State (ISIS) terrorist group has been encouraging would-be attackers to strike during the tournament, spreading propaganda material on its social media channels and via encrypted messaging platform Telegram.
One poster picked up on Telegram and shared on Twitter shows a militant wielding an AK-47 superimposed in front of a stadium and with Russian President Vladimir Putin in the sights of a target. The poster reads, "Putin: You disbeliever. You will pay the price for killing Muslims. Just terror."
Other posters display gruesome invocations of ISIS's practice of beheading its captives, with one showing a balaclava-clad militant standing beside a kneeling Lionel Messi, the Argentinian football champion, in Moscow's Luzhniki stadium.
Such propaganda and graphics are common practice for ISIS, which has used social media and elaborate digital campaigns to reach young recruits and followers around the world. So-called lone wolf attacks have been behind some of Europe's worst terror atrocities in recent years, and are expected to continue as they minimize the cost and organizational effort required of ISIS leadership.