Courtesy the Mawaka family. Elizabeth Mawaka of Hartford, Conn., has sued makers and sellers of chicken jerky dog treats, which she blames for the death of two dogs, including Toby, shown above. She called on Nestle Purina PetCare Co. officials to allow U.S. inspectors to test samples from China plants.

Chinese government officials overseeing plants that make chicken jerky pet treats blamed for thousands of illnesses and deaths among American dogs have refused to allow U.S. inspectors to collect samples for independent analysis, newly released records show.

Investigators with the federal Food and Drug Administration came away empty-handed after conducting April inspections at four jerky treat manufacturing sites in Liaocheng and Jinan, China, according to the records.

The plants make pet treats sold by the St. Louis-based Nestle Purina PetCare Co., including the popular Waggin’ Train jerky brands.

Chinese officials stipulated that FDA officials could collect samples only if they agreed to specific conditions, including a requirement that the samples be tested in Chinese-run laboratories.

As a result, “no samples were collected during this inspection,” wrote Dennis L. Doupnik, an FDA investigator who visited the sites.

In addition, the reports showed that the Chinese plants conducted either no laboratory tests or only sporadic tests of the raw materials, including meat used in treats fed to many of the 78.2 million pet dogs in the U.S.

The FDA found no significant violations and issued no citations, but warned plant owners about problems that included broken supports on metal screens, a torn gasket door on a mixer and failure to file proper paperwork to list actual treat manufacturers instead of shippers or brokers in FDA records.

That means the agency appears to be no closer to solving the mystery of about 2,000 reports of illnesses or deaths in U.S. dogs that ate jerky treats made in China, lawmakers and pet owners said on Tuesday. Despite tests of hundreds of treats in the U.S. over five years, the FDA has found no significant levels of contaminants in the products.

“It’s hard to believe the FDA would send a team of inspectors over to China without first getting a guarantee that they could bring samples back,” said Rep. Dennis Kucinich, D-Ohio, who has been tracking the jerky problem. “They’re doing nothing of consequence. The FDA’s tone-deaf on this one.”

Elizabeth Mawaka, 57, a Hartford, Conn., woman who says her two Boston terriers, Max and Toby, died after eating tainted treats, called on Nestle Purina to demand that samples be released to the FDA.

“It really comes down to the company,” said Mawaka, who is suing jerky treat makers and retailers. “We can talk all we want about China, but it’s really the company.”

However, a Nestle Purina spokesman said the inspections demonstrated no problems with the firm's products and no evidence that they’ve led to illnesses in animals in the U.S.

Keith Schopp, the firm’s vice president of public relations, said that it’s common for countries to refuse to have samples tested outside of the country of origin and that the terms of the inspection were set by the U.S. and Chinese governments, not by Nestle Purina or the manufacturing site officials.

“There was no attempt by Nestle Purina or the Chinese facilities to restrict sample collection,” said Schopp said in an email to NBCNews.com.

"Nestle Purina will continue to cooperate fully with FDA to assist its investigation," added Schopp, who has consistently said the treats are safe to feed as directed.

Tamara N. Ward, an FDA spokeswoman, said in an email that the inspections helped to identify additional areas that the agency may investigate, but there is "no evidence indicating that these firms' jerky pet treats are the cause of pet illnesses in the United States."

Ward did not respond to NBC News questions about the impact of the Chinese officials' refusal to allow FDA to collect samples.

Last November, the FDA issued its third warning since 2007 about potentially dangerous chicken jerky treats after new reports of health problems in dogs surfaced, ranging from diarrhea and vomiting to kidney failure and death. In the months since then, the agency has been swamped with reports of animal illness. Last month, it expanded the caution to include duck and sweet potato jerky treats.

The FDA sent a letter to Chinese officials in March identifying five Chinese firms for inspection. Investigators were sent for several days to each of four plants: Gambol Pet Products Co. Ltd.; Shandong Honva Food Co. Ltd.; and Shandong Petswell Food Co. Ltd., all in Liaocheng, China, and Jinan Uniwell Pet Food Co. Ltd. in Jinan, China, according to reports posted this week on the agency’s animal and veterinary website. The fifth report is pending because of the need for additional information and will be posted later, said Ward, the FDA spokeswoman.

The inspections were pre-arranged and supervised by officials with China’s General Administration of Quality Supervision, Inspection and Quarantine, known as AQSIQ.

AQSIQ officials refused to allow FDA inspectors to collect samples unless they agreed to “certain sampling conditions,” including having the jerky analyzed only in a Chinese government-run laboratory, or a third-party lab in China, wrote FDA investigator Doupnik. FDA investigators would have been allowed to witness the analysis, but not to remove samples.

“I was informed that FDA would not be allowed to ship any samples outside of China for testing in an FDA laboratory due to the issue of national sovereignty among other reasons,” Doupnik added.

Before each inspection, the reports indicated that Doupnik asked AQSIQ officials if their position on the sampling had changed. When he was informed it had not, Doupnik wrote that he did not ask to collect samples during the inspections.

The heavily redacted documents, known as Establishment Inspection Reports, traced the production of jerky treats from raw meat through final packaging. In each case, plant officials said they were aware of few complaints of any kind and none about the treats causing death or illness in dogs. That's despite documented FDA reports of complaints related to each site, Doupnik noted.

At the Shandong Petswell plant, an unidentified plant representative told inspectors that “it is her perception that the firm is making a good product.”

No FDA import alerts or import refusals have been issued for the firms, Ward said. However, she added that the FDA is conducting increased surveillance of shipments of jerky treats from China to provide guidance on possible products to target for sampling and analysis.

But Kucinich said that Chinese officials' refusal to release samples to U.S. inspectors should be grounds for banning the products from import -- or for a mandatory recall.

“That would do it for that product. I would pull them all off the market,” said Kucinich. “Fine. You’re done.”

Consumers have petitioned the FDA to urge Nestle Purina and other jerky treat manufacturers to recall the products. However, FDA officials have said they can’t force a recall based solely on customer complaints.

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