The young man in the video is singing a catchy tune, full of complicated lyrics - and threats: "So come join the ranks/Of the "Islamic State"/A life of obedience/Full of honor and satisfaction and terror to the kafir..." (a derogatory term for non-believers and non-Muslims - ed.).

The message in the video, broadcast online by the jihadist group "Islamic State" (IS), is clear: Those not willing to commit themselves to Islam and submit to its rules will be punished.

The bearer of this "good news," as it's called in the video, is. Silvio K. The 27-year-old is the German face of IS, formerly known as ISIS, until it changed its name a few weeks ago. Born in the eastern state of Saxony, Silvio K. first joined the outlawed Salafist association Millatu Ibrahim in Essen before moving to the branch in the nearby city of Solingen.

At the moment, he is said to be in Syria, where he has called on Western Muslims to join the armed struggle for a caliphate under IS rule. He is also being sought by an international arrest warrant. Whether he has really internalized his own verses is questionable because his lowered eyes during the video suggest that he is reading from a paper.

Silvio K. is known to investigators. "He's a star of the jihadist scene, with an audience of around 5,000-10,000 Salafists in Germany," says terrorism expert Guido Steinberg of the German Institute for International and Security Affairs (SWP) in Berlin. The Islamist is considered dangerous and unpredictable, and has already once threatened to assassinate Chancellor Angela Merkel.

Now, he has once again put German and American security authorities on high alert. In his latest terror threat, Silvio K. has openly called for attacks on Germany. In a letter seen by Germany's Funke Media Group, he calls on "warriors of Allah" to fight against unbelievers in Germany, to "strike a blow they will never forget."

Interior Ministry confirms terror threat

Given the large number of K.'s supporters, security authorities are taking this threat very seriously, not the least because of very specific information on the planned targets. The US atomic bomb storage facility at the Büchel air base in Rhineland-Palatinate is among the targets. According to Funke Media, security has been reinforced around the site, where up to 20 tactical nuclear warheads are kept.

The Ramstein air base is also under heavy guard. In addition to the US facilities, public, private and church bodies in Germany, along with numerous administrative offices and agencies, public transport networks and routes are the extremists' hit list.

Threats in HD quality

Since the outbreak of the Syrian civil war in 2011, German security authorities have logged the departures of about 320 German jihadists to Syria, a number that has risen sharply since last year. Silvio K. was among them.

According to Ahmet Senyurt, a journalist and expert on Islamism living in Germany, the influx of young men can be attributed to a desire to be "part of a revolutionary vanguard."

"The Islamic caliphate of the IS is a social counterpoint to our Western-oriented society," Senyurt told DW. And this, in their eyes, must be defended. "The ideology of the followers of the "Islamic State" may be medieval to our eyes, but they use advanced communication and media strategies." With these advanced methods, the IS is able to connect with those who never really integrated into German society, he said.

Europe's problem

Security experts have warned of the danger posed by the jihadists, should they some day return to Germany, radicalized and with military training. However, Senyurt sees no reason to panic.

"But all the facts support being vigilant and prepared," he said, adding that suicide bombings or attacks, like the one that happened in Brussels in May, are possible. Four people were killed in the Belgian capital, shot by a supposed young Islamist. It's nearly certain that the man had previously participated in Syria's "holy war."

According to Hans-Georg Maassen, Germany's domestic intelligence chief, the Brussels attack is a concrete sign that the return of Syrian fighters has become a European problem, a major challenge for European security agencies.

And, he said, authorities should not focus only on men in their investigations. In early August, Bavaria's intelligence authorities announced the arrest of a woman who had recently returned from Syria. There, she had taken part in the Islamist struggle against the Assad regime, taking her two children with her into the combat zone.