China's product safety agency cast doubt Saturday on claims that a Chinese dumpling maker sickened consumers in Japan, saying tests on its ingredients found none of the insecticide cited by Japanese authorities.

Japanese authorities say dumplings made by the Chinese company, Tianyang Food Processing Ltd., were contaminated with methamidophos, which sickened at least 10 people.

Chinese experts tested 30 ingredients in dumplings from the same batch as those that were exported to Japan, said the General Administration of Quality Supervision, Inspection and Quarantine, or AQSIQ.

"Tests were conducted for such chemicals as methamidophos, and the results showed that without exception nothing was found," the agency said in a one-sentence statement on its Web site. It did not say what other chemicals it tested for.

AQSIQ and other Chinese agencies were sending food experts to Japan to take part in the investigation, the agency said in a separate statement.

The uproar is especially sensitive for China, which is reeling from a series of liability incidents over food, tires and other goods. With the Beijing Olympics starting in August, the government is trying to assure foreign athletes and tourists they will be safe.

China's Agriculture Ministry has banned the use of methamidophos since Jan. 1, 2007, but the country had large stockpiles and it is unclear whether farmers might still use it.

The case is unusual because Chinese food processors that export to Japan are regarded as industry leaders in quality and safety. They are inspected regularly by Japanese officials to enforce Tokyo's quality standards, which are among the world's most stringent.

On Saturday, the manager of Tianyang's factory said its ingredients are regularly tested and no pesticide residue has been found. He said products were sealed at the factory and shipped directly to Japan.

"There is no chance of contamination during transportation inside China," the manager, Di Menglu, said at a news conference in Shijiazhuang, a city southwest of Beijing. "All products were fully heated for sterilization and fully in accordance with the sanitary standards of China and Japan."

Di's comments were the company's first public statement on the incident.

The Japanese government says 10 people were sickened and news reports say as many as 500 people might be affected.

A Japanese spokesman this week blamed "loose safety awareness" on the Chinese side for the poisonings.

Japanese investigators said Friday, however, that they found a tiny hole in a dumpling bag recovered from a sickened family, suggesting the food may have been deliberately contaminated.

The dumpling incident was widely reported in Japan and prompted many stores and restaurants to stop using Chinese food, reconsider safety standards and cut back on business with China.