WASHINGTON (Reuters) - FBI Director Robert Mueller visited Libya on Thursday, an FBI official said, as U.S. investigators continued their inquiry into the September attack in Benghazi in which U.S. Ambassador to Libya Christopher Stevens and three other Americans died.

"The director's visit was an opportunity to discuss ongoing cooperation on a number of issues," said the FBI official, who spoke on condition of anonymity.

(Reporting by David Ingram; Editing by Vicki Allen)