WASHINGTON, Dec 6 (Reuters) - U.S. Secretary of State Antony Blinken spoke to Ukraine President Volodymyr Zelenskiy on Monday ahead of President Joe Biden"s call with Russian President Vladimir Putin, during which he is expected to warn Russia of severe economic consequences should Russia go ahead with a invasion of Ukraine. State Department spokesman Ned Price told reporters that the United States remains committed to NATO"s open door policy and that the alliance should remain ready to aspirants when they"re ready. Ukraine, a former Soviet republic, now aspires to join the European Union and NATO.