Reuters reports Iran will respond with equal countermeasures if the United States tries to block its oil exports, the foreign ministry in Tehran said on Tuesday. U.S. officials are stepping up diplomatic efforts to pressure countries to stop importing Iranian oil “Supreme Leader Ayatollah Ali Khamenei on Saturday backed President Hassan Rouhani’s suggestion that Iran might block Gulf oil exports if its own exports are stopped. Already fraught relations between Tehran and Washington have worsened in recent days.