(Corrects last paragraph to say that one Sun Pharma plant and some Wockhardt plants have been barred from exporting drugs to the US. The incorrect version suggested that all Sun Pharma and Wockhardt plants were barred)

April 1 (Reuters) - The U.S. Food and Drug Administration found contamination of drug ingredients manufactured at a GlaxoSmithKline Plc plant in Ireland and said the company did not take sufficient action to resolve the problems.

The news comes just days after GSK said it was recalling all supplies of its over-the-counter weight-loss drug in the United States and Puerto Rico, after concerns that bottles had been tampered with.

In a warning letter dated March 18, the U.S. FDA said GSK did not fully investigate a list of objectional conditions the regulator sent after its inspection of the manufacturing plant at Cork, Ireland in October.

The FDA said its investigator found that a certain drug ingredient, the name of which was not disclosed, was contaminated with material from the plant's pharmaceutical waste tank. (http://link.reuters.com/xah28v)

Some batches of a drug or drugs using the contaminated ingredient were later shipped, the FDA said, and GSK did not notify its customers about the lapse.

The investigator also raised concerns about the suitability of the equipment used to manufacture the ingredients.

The FDA said it might withhold approval of any new drug applications that list GSK as the manufacturer of their drug ingredients until GSK corrected the issues.

The regulator said it also might refuse the import of drugs manufactured at the Cork facility into the United States.

GSK was not immediately available for comment.

The FDA has stepped up its efforts to ensure drug safety in recent months, banning drugs and drug ingredients imported from Indian manufacturers over quality concerns.

Ranbaxy Laboratories Ltd has been banned from exporting drugs from its Indian plants to the United States. One of Sun Pharmaceutical Industries Ltd's plants and some of Wockhardt Ltd's plants have also been barred from exporting to the United States.

(Reporting by Vrinda Manocha in Bangalore; Editing by Maju Samuel)