Police on Thursday arrested a German-Tunisian man suspected of having joined the Islamic State (IS) jihadist group in Syria, the federal prosecutor's office said.

The 26-year-old suspect, named as Ayub B., is thought to have entered Syria via Turkey last year to be trained in IS combat and recruiting, before returning to Germany in August, the German prosecutor said in a statement.

The German authorities have not uncovered any evidence of concrete preparations for an attack on their soil.

Berlin estimates that some 550 German nationals have gone to fight in IS ranks in Syria and Iraq.