US has warned Iran of new and serious consequences, if all unjustly detained American citizens are not released and returned. <br/><br/>White House said in a statement that President Donald Trump urged Iran to return Robert Levinson, an American former law enforcement officer who disappeared more than 10 years ago in Iran, and demanded that Tehran release businessman Siamak Namazi and his father, Baquer. <br/><br/>The statement said Trump and his administration are redoubling efforts to bring back all Americans unjustly detained abroad.