WASHINGTON (Reuters) - U.S. Treasury Secretary Steve Mnuchin said on Wednesday that if the United Nations does not put additional sanctions on North Korea over nuclear tests, he has an executive order ready for President Donald Trump to sign that would impose sanctions on any country that trades with Pyongyang.  I have an executive order prepared. It s ready to go to the president. It will authorize me to stop doing trade, and put sanctions on anybody that does trade with North Korea. The president will consider that at the appropriate time once he gives the U.N. time to act,  Mnuchin told reporters on a flight back to Washington from North Dakota, where Trump gave a speech on tax reform. 