Traces of the industrial chemical melamine have been detected in samples of top-selling US infant formula, but federal regulators insist the products are safe.

The Food and Drug Administration said last month it was unable to identify any melamine exposure level as safe for infants, but a top official said it would be a "dangerous overreaction" for parents to stop feeding infant formula to babies who depend on it.

"The levels that we are detecting are extremely low," said Dr. Stephen Sundlof, director of the agency's Center for Food Safety and Applied Nutrition. "They should not be changing the diet. If they've been feeding a particular product, they should continue to feed that product. That's in the best interest of the baby."

Melamine is the chemical found in Chinese infant formula - in far larger concentrations - that has been blamed for killing at least three babies and making at least 50,000 others ill.