(Reuters) – An Italian supplier at the center of recent industrial snags on the 787 Dreamliner airplane produced more than 4,000 noncompliant parts destined for Boeing Co. over five years, a preliminary report from Italian prosecutors shows.

Initial results of an investigation launched earlier this year suggest that Manufacturing Process Specification, or its now-bankrupt predecessor company Processi Speciali, produced flawed parts between 2016 and 2021, according to the document.

According to the report, seen by Reuters, the suspect titanium parts made it into 35 Boeing 787 fuselages.

It added that the Brindisi-based supplier also made parts for the Boeing 767, a freighter model which is now also used as the basis for a U.S. Air Force tanker.

The investigation aims to establish whether MPS or its predecessor firm produced flawed components that could threaten air safety, a risk that has been denied by Boeing.

Boeing declined direct comment on the prosecutors' document, parts of which were first reported by Italian daily Il Corriere del Mezzogiorno. It reiterated, however, that airworthiness had not been affected.

"While our assessment is ongoing, this does not present an immediate safety of flight concern," a spokesperson said.

In October, Boeing said some 787 Dreamliner parts supplied by MPS had been improperly manufactured over the previous three years, marking the latest in a series of industrial snags to hit the airliner.

Italy's Leonardo, which was the immediate customer for parts made by MPS and has said it too is a victim of the suspected failure to meet specifications, declined comment.

A lawyer for former MPS Chief Executive Antonio Ingrosso, as well as for the former chief executive of its now-bankrupt predecessor Processi Speciali, also declined to comment.

The U.S. Air Force did not immediately respond to a request for comment on whether suspect parts had reached any of its 767-based KC-46 tankers, the first of which was delivered in 2019.