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 FDA said the company did not fully investigate a list of objectional conditions the regulator sent after its inspection of the manufacturing facility 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 facility's pharmaceutical waste tank.