By Idrees Ali and Phil Stewart WASHINGTON (Reuters) -The United States has seen indications that Russia’s military in its assault on Ukraine is using so-called dumb bombs that are unguided and greatly increase the risk of missing targets, a senior U.S. defense official said on Wednesday. “We do have indications that the Russians are in fact dropping some dumb munitions,” the official told reporters, speaking on condition of anonymity, adding that the United States was observing “increasing damage to civilian infrastructure and civilian casualties.” The comments came shortly after Ukraine accus…