Less than two months after federal food regulators said they were unable to set a safety threshold for the industrial chemical melamine in baby formula, they announced a standard that allows for higher levels than those found in U.S.-made batches of the product.

Food and Drug Administration officials on Friday set a threshold of 1 part per million of melamine in formula, provided a related chemical isn't present. They insisted the formulas are safe.

The setting of the standard comes days after The Associated Press reported that FDA tests found traces of melamine in the infant formula of one major U.S. manufacturer and cyanuric acid, a chemical relative, in the formula of a second major maker. The contaminated samples, which both measured at levels below the new standard, were analyzed several weeks ago.

The FDA had stated in early October that it was unable to set a safety contamination level for melamine in infant formula.

Dr. Stephen Sundlof, FDA's director of food safety, said Friday the agency was confident in setting the 1 part per million level for either of the chemicals alone. although there has been no new scientific studies since October that would give regulators more safety data. He had no ready explanation for why the level wasn't set earlier.

The standard is the same as the one public health officials have set in Canada and China where in September the problem of melamine in infant formula first surfaced. But it is 20 times higher than the most stringent level in Taiwan.

Sundlof said the lack of dual contamination was key because studies so far show dangerous health effects only when both chemicals are present. He emphasized that neither of the two tainted samples had both contaminants.

The agency still will not set a safety level for melamine if cyanuric acid is also present, he said.

Both the new safety level and the amount of the chemical found in U.S.-made infant formula are far below the amounts of melamine added to infant formula in China that have been blamed for killing at least three babies and making thousands ill.

"The levels were so low ... that they do not cause a health risk to infants," Sundlof said. "Parents using infant formula should continue using U.S.-manufactured infant formula. Switching away from one of these infant formulas to alternate diets or homemade formulas could result in infants not receiving the complete nutrition required for proper growth and development."

Reacting to news of the contaminated formulas, members of Congress, a national consumer group and the Illinois attorney general have demanded a national recall, something the FDA said made no sense because it had no evidence suggesting that the formula would be dangerous for babies at the levels of contamination found.

After saying it made an error in its data, the FDA on Wednesday produced these results: Nestle's Good Start Supreme Infant Formula with Iron had two positive tests for melamine on one sample; Mead Johnson's Infant Formula Powder, Enfamil LIPIL with Iron had three positive tests on one sample for cyanuric acid.

Separately, a third major formula maker, Abbott Laboratories, told the AP that in-house tests had detected trace levels of melamine in its infant formula.

Those three formula makers manufacture more than 90 percent of all infant formula produced in the United States.

The FDA said it had analyzed 74 samples and was continuing to examine 13 more.

The agency had left the impression of a zero tolerance on Oct. 3 when it stated: "FDA is currently unable to establish any level of melamine and melamine-related compounds in infant formula that does not raise public health concerns."

The FDA and other experts said they believe the melamine contamination in U.S.-made formula had occurred during the manufacturing process, rather than intentionally. The U.S. government quietly began testing domestically produced infant formula in September, soon after problems with melamine-spiked formula surfaced in China.

Melamine can legally be used in some food packaging, and can rub off into food from there. It's also part of a cleaning solution used on some food processing equipment.

There is a gap between the concentration that the FDA detected in formula and the agency's estimate of how much melamine could contaminate food from the manufacturing process. The expected contamination from processing — 15 parts per billion — is about one-tenth the amount that the agency has detected in infant formula. FDA officials have not responded to questions from the AP this week about how that gap might be explained.

The agency said it is continuing research on animals to see the effects of ingesting both melamine and cyanuric acid.