There was no known motive for the shooting in Germany's third-largest city, which went into lockdown with transport halted and highways sealed off immediately after the attack on Friday evening. *** German Foreign Minister Frank-Walter Steinmeier said the motive for the attack was not yet clear. "The motives for this abhorrent act have not yet been completely clarified - we still have contradictory clues," he said in a statement. There was no immediate claim of responsibility but supporters of Islamic State celebrated on social media. "The Islamic state is expanding in Europe," read one tweet.