WASHINGTON (Reuters) - U.S. President Joe Biden said on Thursday he had authorized another $800 million in military aid for Ukraine, citing a "critical window" in the conflict as Russia sets the stage for the next phase in the war.

       He said the new package will include heavy artillery, 144,000 rounds of ammunition and tactical drones.

       (Reporting by Patricia Zengerle; Editing by Chizu Nomiyama)