A man carrying a gas cylinder walks out of the research and development centre of Sun Pharmaceutical Industries Ltd in Mumbai May 29, 2014. REUTERS/Danish Siddiqui

MUMBAI (Reuters) - Sun Pharmaceutical Industries Ltd, India’s largest drugmaker, said on Wednesday the U.S. health regulator has informed the company of more concerns found at its Halol manufacturing plant after a recent inspection.

The approval of several of Sun’s key drugs in the United States, the drugmaker’s biggest market, depends on the clearance on its Halol plant in the western Indian state of Gujarat. A warning letter issued by the U.S. Food and Drug Administration (FDA) last year over violations found at the plant has already been hurting the company’s sales.

The latest notice, a Form 483, was issued to Sun after the FDA completed an inspection of the Halol plant on Dec. 1, the company said. Such a notice is issued when the FDA finds that conditions at a drug plant violate U.S. rules.

It is unclear what violations the FDA found. Sun did not disclose them, and the FDA does not typically make such findings public.

The company’s stock took a beating on Wednesday after Indian brokerage IIFL said in a note to clients it was aware that the FDA’s findings on the Halol plant ran 14 pages long. Sun, in its statement, did not comment on the length of the notice. It said it was working on responding to the letter within 15 days.

Sun’s shares were down 5.3 percent at 0827 GMT in Mumbai.