The company said the FDA's letter, dated Nov. 9, followed a regulatory inspection of its Morgantown, West Virginia plant in April.

As a result of the company's ongoing restructuring at the facility, Mylan said there is a temporary disruption in supply of certain products and it has discontinued some products and transferred others to different facilities.

The company did not specify which products were affected. In April, Mylan announced layoffs of about 15 percent of its workforce at the same plant.

The letter https://www.fda.gov/ICECI/EnforcementActions/WarningLetters/ucm626360.htm from the FDA, also posted on the agency's website on Tuesday, highlighted an "inadequate" cleaning program for manufacturing equipment and said Mylan failed to thoroughly investigate unexplained discrepancies or batches of medicines that failed to meet specifications.

Failure to rectify the FDA's concerns could result in the agency taking legal action, it said.

While the letter is a setback, it is unlikely to impact Wall Street estimates for the company's performance this year, analysts said.

Before receiving the letter, Mylan had a "pristine" regulatory track record with no FDA warning letters at its largest manufacturing facility in Morgantown since establishing the plant in 1966, Raymond James analyst Elliot Wilbur said.

"It is unclear how long the issues will take to resolve and even what the immediate upside impact could be ... (still) management indicated that none of its key expected new product launches during 2019 were filed from the Morgantown facility," he said.

Mylan's shares fell about 2 percent to $33.91 after the bell on Tuesday.

Earlier in the day, the company said it would recall certain batches of blood pressure medicine valsartan in the United States after they were found to contain a probable cancer-causing impurity, a day after European regulators stepped in to ban the products.

(Reporting by Tamara Mathias in Bengaluru; Editing by Maju Samuel)