Argentina's relations with the U.S. worsened sharply Monday as the South American country continued to hold military equipment it confiscated last week from a U.S. Air Force C-17 transport plane sent as part of a training course for local police. U.S. Assistant Secretary of State for Western Hemisphere Affairs, Arturo Valenzuela, called on Argentina to return the property without delay. "It's absolutely necessary that they immediately return that material. It makes no sense for it to have been confiscated this way. This material was intended for a joint exercise in training people to rescue hostages," Mr. Valenzuela Monday said on...