WASHINGTON - US officials have found trace amounts of melamine in a single sample of infant formula made in the US, but believe the contamination resulted from the manufacturing process and was not intentional, CNN reported on Wednesday.

Of 77 samples tested, one contained traces of melamine, FDA spokesman Judy Leon told CNN. A reading of less than 250 parts per billion is considered trace.

Last month, the Food and Drug Administration (FDA) said melamine at 2,500 parts per billion is safe in foods other than infant formula. The agency said it did not have enough data to set a limit for infants.

Melamine, an industrial chemical, is not found in nature. It is used to line cans, make flame retardant and cleaning products.

CNN said Ms Leon would not say who made the contaminated formula, but added it had likely been contaminated while being manufactured or through the can liners.

The FDA also found trace levels of melamine in several samples of medical formula given to the elderly, but at levels that posed no health risk, Ms Leon said.

At least four children have died of kidney failure and 53,000 have fallen ill in China this year after consuming milk or dairy products laced with melamine.

The dairy scandal has expanded worldwide with several governments recalling or banning Chinese products with milk content. -- AFP