July 22 (Reuters) - The U.S. National Transportation Safety Board said on Wednesday it has not ruled out age or service issues in a probe into an incident in which a passenger was partly sucked out of a Boeing 737 NG BA.N broken window.

The letter contradicted Ryanair RYA.I CEO Michael O'Leary who said on Monday an initial finding from the probe suggested "foreign object damage" and was not due to the aircraft's age or servicing conditions.

"The NTSB has not made any such determination," NTSB Chair Jennifer Homendy wrote in a letter to O'Leary, adding the CEO's comments had violated the agency's rules on disclosure by parties to the investigation.

Ryanair did not immediately respond to a request for comment.