ZURICH, Dec 17 (Reuters) - The Swiss National Bank kept its ultra-expansive monetary policy on hold on Thursday, keeping the world’s lowest interest rates and readiness to launch currency interventions despite being labeled a currency manipulator by the United States. The SNB kept its policy rate locked at minus 0.75%, as unanimously forecast by economists in a Reuters poll. It also kept the interest rate it charges commercial banks on some deposits they park overnight with the central bank at minus 0.75%, as expected.