U.S. inflation increased at its fastest pace in three years in April, driven by higher energy prices due to the Iran war and cementing economists' views that the Federal Reserve would hold interest rates unchanged well into next year. Surging price pressures are eroding household income and threatening to restrain consumer spending and economic growth this year. Income at the disposal of households after adjusting for inflation dropped for a third straight month in April, with the saving rate hitting a four-year low, other data from the Commerce Department showed on Thursday.