By Jeff Mason, Alexandra Alper and Trevor HunnicuttWEST MIFFLIN, Pennsylvania (Reuters) -U.S. President Donald Trump on Friday lauded an "agreement" between Nippon Steel and U.S. Steel at a political rally but stopped short of clarifying whether he planned to approve the companies' diplomatically sensitive merger.

President Donald Trump was all set to hold a rally in Pennsylvania on Friday to celebrate a details-to-come deal for Japan-based Nippon Steel to invest in US Steel, which he says will keep the iconic American steelmaker under US-control.