Drugmaker Mylan Inc refuted a newspaper report its staff overrode government-mandated quality controls, saying the report was based on improperly obtained documents, uninformed third-party commentary and anonymous sources.

The Pittsburgh Post-Gazette newspaper had said workers at Mylan overrode quality controls intended to ensure the safety and effectiveness of prescription drugs, citing an internal report.

The Post-Gazette said the practice of violating government-mandated quality control procedures at the generic drugmaker was pervasive and occurred on all three shifts at the company's plant in Morgantown, West Virginia, which makes roughly 19 billion doses of medication annually.

It said Mylan has launched a probe into the matter.

Simply put, our investigation of the issue demonstrates that our quality systems are working, not the contrary, Mylan said in a statement.

Mylan spokesman Michael Laffin had said in an email to Reuters on Sunday that the issue cited in the Post-Gazette had no impact on product quality whatsoever. Laffin said that like any manufacturing facility, Mylan periodically faces deviations in standard operating procedures.

What sets us apart is the way we've always addressed these issues, swiftly and effectively, Laffin wrote.

Spokesmen for the Food and Drug Administration did not respond to messages left by Reuters seeking comment.

The Post-Gazette said in its report it was unclear exactly how long employees had been ignoring so-called red screens, alerts triggered during the making of tablets and capsules that warn production workers that the medication may not meet specifications.

Experts interviewed by the newspaper, who reviewed the internal report, said there was not enough information to judge whether any drugs going out the door had been compromised.

(Reporting by Steve Eder in New York and Ajay Kamalakaran in Bangalore; Editing by Leslie Adler and Valerie Lee)