German federal prosecutors on Monday took over a probe into the deadly knife assault in a Hamburg supermarket, after finding that the attacker likely had a "radical Islamist" motive.

"It appears that there is a radical Islamist background to the act. According to ongoing investigations, the accused had self radicalised," said federal prosecutors in a statement, adding that there are no indications that the 26-year-old man named as Ahmad A. was a member of a jihadist group like the Islamic State organisation.