(Reuters) – A Russian flight was en route to Washington on Saturday to collect Russian diplomats who were expelled this week from their posts at the United Nations over U.S. national security concerns, officials said. Russia denies the allegations and says it will retaliate for their expulsion. A Rossiya Special Flight Squadron is flying to Washington from St. Petersburg to bring the diplomats to Russia, foreign ministry spokesperson Maria Zakharova said. “This plane will bring back home the Russian diplomats whom the Government of the United States has declared personae non grata,” Zakharova …