German police arrested a suspected supporter of the insurgent group Islamic State (IS) who was recently in Syria and raided his apartment in the state of North Rhine-Westphalia, federal prosecutors said on Sunday.
The 24-year-old suspect, who has German citizenship, was suspected of having joined Islamic State during a stay in Syria from October 2013 until November 2014, a spokeswoman of the federal prosecutor general said.
There were no indications, however, that the man identified as Nils D. had concrete plans for an attack and there was also no connection to the Jan. 7-9 Islamist militant attacks in Paris in which 17 people were killed, she said.
The arrest took place on Saturday in the city of Dinslaken.
As with other west European countries, Germany is struggling to stop the radicalisation of young Muslims, some of whom want to become jihadist insurgents in Syria or Iraq. Officials also worry that they might return to plot attacks on home soil.
German intelligence authorities estimate that at least 550 people have left Germany for Syria and around 180 have returned. Many are under criminal investigation.
Wednesday's deadly attack on French satirical magazine Charlie Hebdo has fuelled fears of assaults on similar targets also in other European countries.
According to a report in the mass-circulation Bild am Sonntag newspaper, Western intelligence agencies have tapped conversations of senior Islamic State members in which they said the Paris attack was the start of a series in Europe.
Earlier on Sunday, a building of German newspaper Hamburger Morgenpost was the target of an arson attack and two suspects were arrested, police said. Like many other newspapers, the Hamburg daily re-printed cartoons from Charlie Hebdo after the attack on Wednesday in Paris.