U.S. Secretary of State warned Venezuela on Thursday that it would be "a very bad day" for the South American country if it were to attack its neighbor Guyana or U.S.-based energy giant ExxonMobil , in comments that threatened unspecified action in such a case.

Secretary of State Marco Rubio was visiting Guyana amid ExxonMobil’s oil production there. Venezuela has asserted claims to a large region of the country. Mr. Rubio later flew to Suriname.

US Secretary of State Marco Rubio warned Venezuela that any attempt to invade Guyana or threaten Exxon Mobil Corp.’s operations in the country would be a “very bad move.”