Turning the tables on the United States amid growing worries over dangerous Chinese products, Beijing said Friday some health supplements and raisins imported from the U.S. failed to meet China's safety standards and have been returned or destroyed.

In Washington, a top U.S. food safety official said the Food and Drug Administration was seeking more information from its Chinese counterparts, including whether they are "bona fide, science-based findings" or in retaliation for U.S. actions.

U.S. inspectors recently have banned or turned away a growing number of Chinese exports, including monkfish containing life-threatening levels of puffer fish toxins, drug-laced frozen eel and juice made with unsafe color additives. The FDA has also stopped all imports of Chinese toothpaste to test for a potentially deadly chemical reportedly found in tubes sold in Australia, the Dominican Republic and Panama.

Friday's announcement said Chinese inspectors in the ports of Ningbo and Shenzen found bacteria and sulfur dioxide in products shipped by three American companies.

"The products failed to meet the sanitary standards of China," the General Administration of Quality Supervision, Inspection and Quarantine said in a notice posted on its Web site.

No details were given on when or how the inspections were conducted and telephones at the administration's office were not answered Friday.

The companies were identified as K-Max Health Products Co., CMO Distribution Center of America Inc., and Supervalu International Division.

The agency said K-Max and CMO exported health capsules, including bee pollen and bacteria-fighting supplements. Supervalu exported Sun-Maid Golden Raisins, it said. The shipments from K-Max and Supervalu have been destroyed and CMO's capsules were returned, the notice said.

The FDA's assistant commissioner for food protection, Dr. David Acheson, said U.S. officials were seeking more information.

"Whatever the motives are for this, if it's real, we want to know about it," Acheson said.

"Is it tit-for-tat? We don't know and probably won't ever know. If they found a legitimate problem with a product exported from the United States, we would want to know about it so we can look into it and fix it."

Depending on what the FDA learns, it could follow up with inspections of the companies and its own sampling and testing, Acheson said. Previously, the agency hasn't known of any problems with the companies' products flagged by the Chinese, he added.

Neil Langerman, an officer of the division of chemical health and safety of the American Chemical Society, questioned whether China's seizure was in retaliation for recent U.S. actions against Chinese products.

"There's more to this story than meets the eye. This is political," said Langerman, an officer of the division of chemical health and safety of the American Chemical Society. "I'd see what China is doing as a retaliation to what the U.S. has done."

The Chinese announcement did not specify which contaminants were found in which products, saying only that they were found in amounts above acceptable levels, without providing details.

"Local quality officials should step up the inspection and quarantine on imported food products from the U.S.," the Chinese notice said. "Chinese importers should also clarify food safety demands in contracts when importing U.S. food products, so as to lower the trade risk."

Langerman said only a very small percentage of U.S. food shipments have bacterial problems.

"Without seeing data, the claims, while they may in fact be valid, don't have merit," he said. "I as a scientist say, show me your data, not only your data, but how you sampled it. Did you use sterile collection techniques?"

Langerman said sulfur dioxide can be present in raisins, but said companies would not use it at high levels because it adds an eggy odor. "It's also easy to get rid of because it's a gas, so you let it dissipate," he said.

Marion Nestle, a nutrition professor at New York University, said she didn't know why sulfur dioxide would pose a problem, since it's often used to preserve raisins and other dried fruit. She said raisins would be an unlikely host to bacteria because they are dry.

"This looks like retaliation," she said, noting that the Chinese have complained that American authorities are holding their exports to food-safety standards that were never detailed.

As for the herbal supplements, Nestle said the notice was too vague to know what might be in them, though she noted the Chinese are significant exporters of herbal supplements.

Friday's announcement was the second mention in recent days of China rejecting foreign food imports. Late last month, France's Groupe Danone SA said China seized five containers of Evian water in February because of concern over high bacteria levels.

Those came after concerns spiked over the safety of Chinese food exports following the deaths of cats and dogs in the United States and Canada blamed on tainted pet food ingredients from China.

K-Max president Liei Ye did not immediately respond to a message left with the company Friday seeking comment. K-Max is a subsidiary of Kang Long Group Corp., whose Web site said the company began by selling Wisconsin-grown ginseng to U.S. health food stores under its K-Max brand, before expanding into China, Russia, Japan, Korea, Hong Kong, Taiwan and other markets. Kang Long has four mainland China offices and a Hong Kong branch in addition to its Pomona, Calif., headquarters, according to the site.

Supervalu International is part of Supervalu Inc., headquartered in Eden Prairie, Minn. The FDA said in 2000 that CMO Distribution Center of America was based in Sarasota, Fla. However, state records showed it was dissolved as a company in Florida in 2003.