The US Food and Drug Administration has imposed an "import alert", effectively a ban, on the Chikalthana plant operated by Indian generic drugmaker Wockhardt Ltd, the regulator said in a notice on its website, sending the company's shares down as much as 13.5 per cent.

An "import alert" results in the detention without physical examination of drugs from firms that have not met so-called good manufacturing practices, according to the

FDA website.

A spokesman for Wockhardt was not available for comment.

The latest FDA action against Wockhardt comes amid a slew of regulatory rebukes this year. Its factory in Chikalthana in western India was last month hit by the British drug regulator's curb on imports from the plant over manufacturing deficiencies.

Indian firms, which make nearly 40 per cent of generic and over-the-counter drugs for the US market, are facing more regulatory woes, including a record fine for Ranbaxy Laboratories, amid increased scrutiny by overseas regulators.