ISIS supporters threaten Mark Zuckerberg, Twitter's Jack Dorsey - CNET

ISIS supporters have a new target in their sights: the leaders of two of the world's most popular social networks.

The "Sons Caliphate Army," a group of hackers associated with the militant Islamic group, posted a video Tuesday that shows photos of Facebook's Mark Zuckerberg and Twitter's Jack Dorsey engulfed in flames and as targets for bullets. The 25-minute video, titled "Flames of the Supporters," is said to have been authenticated by Storyful, a startup that focuses on verifying news coming from the social Web.

The two tech leaders are apparently being singled out for their efforts to combat terrorist activities on their respective social networks. Both Facebook and Twitter in recent months have announced campaigns to eliminate activities by Islamic State extremists on their platforms by suspending accounts and deleting posts that promote violence and terrorism.

The stepped-up policing came about a month after a handful of leading tech companies met with top federal law enforcement and security officials in Silicon Valley to discuss combating terrorism. The meeting was called after attackers inspired by the Islamic State killed more than 130 people in Paris and 14 people in San Beardino, Califoia.

With hundreds of millions of people logging in each day, Islamic State and other radicals have found social media to be a fertile recruiting ground. In response, social networks have increased the size of teams overseeing posts and traffic.