WASHINGTON (Reuters) - Senior U.S. officials are advising Ukraine to hold off on launching a major offensive against Russian forces until the latest supply of U.S. weaponry is in place and training has been provided, a senior Biden administration official said on Friday.The official, speaking to a small group of reporters on condition of anonymity, said the United States was holding fast to its decision not to provide Abrams tanks to Ukraine at this time, amid a controversy with Germany over tanks.U.S. talks with Ukraine about any counter-offensive have been in the context of ensuring the Ukrainians devote enough time...