The Syrian citizen was detained in a "concentrated police action" and is facing a thorough investigation, authorities said Tuesday. The police indentified him as Malik F., a doctoral student based in Darmstadt.

Malik first drew public attention earlier this week when his online video started making rounds on social media.

In the clip, Malik explains why he "supports and defends" the "Islamic State" (IS) group.

The Darmstadt student accuses the US, "the figurehead of heresy," of the systematic extermination of Sunni Muslims, and describes the rulers of Saudi Arabia and rulers of other their Arab allies as "worse than pigs."

He also accuses the Saudis and the Free Syrian Army of trying to "appease the infidels" and being "funded by the infidels."

In the Arabic-language video, Malik also defends IS's burning of the Jordanian pilot and its stoning of women accused of adultery, saying that the acts were justified by Sharia law.

Islamic State is "in the right, I say, because they rule by the Sharia of our Lord," he concludes.

A spokeswoman for the German domestic intelligence service described the clip as "jihadist propaganda."

'I love Germany'

The video, which was recently discovered and translated into English by the US-based Middle East Media Research Institute, came as a surprise to his colleagues in Darmstadt.

Malik was "respected as a colleague" and never "drew attention with extremist attitudes" said the Technical University spokesman Jörg Feuck to the newspaper, "Die Welt."

According to the "Welt" report, the mathematician arrived in Germany in 2007, and was the recipient of a Syrian government scholarship for his PhD in mathematics until 2011.

"I love Germany" Malik stated just hours before his arrest, when contacted by reports from the regional broadcaster Hessische Rundfunk.

When asked if he approved of stoning of women, Malik answered: "That is our religion, I think our religion is good, of course."

Spreading IS propaganda has been punishable by law in Germany since September 2014.