Adds more details, no immediate Boeing comment, more details in paragraphs 4-8

By David Shepardson

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 after an uncontained engine failure.

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, and our investigators have not yet ruled out age or servicing issues as contributing to this event," 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. She urged him to refrain from making further public statements regarding the probe.

Ryanair and Boeing did not immediately respond to requests for comment.

The NTSB is investigating the July 10 incident, in which ​a piece of the engine broke off the aircraft and ⁠smashed the window shortly after takeoff from Thessaloniki in ​Greece, according to video and the Federal Aviation Administration. The ​plane, headed to Germany, lost pressure and made an emergency landing.

"Initial indication would suggest it looks like a foreign object damage to the ​engine on takeoff at Thessaloniki, but we don't have, we ​can't say that definitively," O'Leary told analysts.

O'Leary ⁠said the aircraft was 18 years old and its engine had been fully serviced and overhauled within the last two years. He added that a draft report on the incident ​would be ​issued in about ⁠28 days, followed by a more detailed report.

The event, which had echoes of two Southwest ​Airlines LUV.N Boeing 737 NG flights in 2016 ​and 2018, ⁠prompted a re-evaluation of the response to those incidents, FAA Administrator Bryan Bedford told Reuters last week, adding: "I don't think the early indications are ‌that (the ⁠recent Ryanair problem) mimics what the Southwest incident was."