NEW YORK, June 17 (Reuters) - A unit of Merck & Co Inc has agreed to pay $5.9 million to resolve claims that it fraudulently promoted a drug used to treat pink eye for unapproved purposes, U.S. authorities announced on Wednesday.

Manhattan U.S. Attorney Preet Bharara said Inspire Pharmaceuticals, which Merck acquired in 2011, promoted its drug AzaSite to healthcare providers for uses the Food and Drug Administration had not approved as safe and effective.

(Reporting by Nate Raymond in New York; Editing by Chris Reese)