GEORGETOWN, Guyana (Reuters) - It would be "a very bad day" for Venezuela if it were to attack its neighbor Guyana or U.S.-based energy giant ExxonMobil, U.S. Secretary of State Marco Rubio said on Thursday during a visit to Guyana's capital.

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.

The US Secretary of State considers Caracas’ sovereignty claims over the Essequibo region to be illegitimate, and expresses support for the small oil-rich nation where ExxonMobil operates