ATHENS (Reuters) - A senior U.S. State Department official on Wednesday repeated warnings from Washington that Greece had to make a "serious move" to break a deadlock with its international creditors. Deputy Assistant Secretary for European and Eurasian Affairs Amanda Sloat met Greek Alternate Foreign Minister Euclid Tsakalotos and reaffirmed recent messages from President Barack Obama and Treasury Secretary Jack Lew, a statement from the U.S. embassy in Athens said. ...