Tests show a second type of pesticide in dumplings made by a Chinese company whose products have sickened at least 10 people in Japan and set off a nationwide panic over food safety, a supermarket chain said Wednesday.

Japanese Consumer's Cooperative Union, a retailer, said tests detected the chemical dichlorvos in both the filling and dough of frozen dumplings made in June by China's Tianyang Food Processing Ltd.

Tianyang is the producer of dumplings contaminated with the pesticide methamidophos and blamed for a string of illnesses in western and central Japan since December.

China and Japan have sent teams of investigators to each other's country in recent days to determine the cause of the methamidophos contamination, which some Japanese officials suspect may have been deliberate.

While it was not immediately clear whether the two contaminations were related, the latest disclosure heightened fears in Japan over the safety of products from China, a growing source of cheap foods in high-priced Japan.

"The most important task is to prevent damage from spreading and all we can do is to find out what was the cause and what really happened," Japanese health minister Yoichi Masuzoe said Wednesday. "What we need primarily is cooperation between Japan and China."

The two countries have agreed to set up contact points to share information, Shigeru Hotta, assistant vice minister for quality of life policy at Japan's Cabinet Office, said during a news conference wrapping up talks between Japanese and Chinese food safety officials in Tokyo.

"We agreed to cooperate and find out what caused the problem quickly," said Li Chunfeng, the head of Chinese delegation. "I swear that Chinese food is safe," he added.

In the dichlorvos contamination, the dumplings were recalled after a worker at one of the consumer union's outlets complained of oil-like odor in November, the union, widely known as Co-op, said in a statement Tuesday.

Tests conducted by Co-op this week found traces of dichlorvos, the union said. Previous tests late last year on the dumplings' packaging had found traces of other chemicals, but no pesticide tests were conducted.

A total 10 parts per million of dichlorvos was detected from the dumplings -- 110 ppm in the dough and 0.42 ppm in the filling, according to Co-op's statement. Japanese residue standards for wheat is 1 ppm and 0.1 ppm for cabbage, one of the ingredients for the filling.

A Co-op spokeswoman, speaking on condition of anonymity, confirmed the findings Wednesday.

There have been no reports of health problems stemming from dumplings made on the same day -- June 3, 2007-- but the concentration level of the insecticide is above the level that is acceptable for a person weighing 50 kilograms (110 pounds) if two dumplings are consumed, Japanese daily Asahi reported.

Meanwhile, Japan Tobacco said that it has scrapped a planned merger of its frozen food operations with noodlemaker Nissin after the tobacco company's affiliate -- JT Foods Co. -- announced recalls of dumplings and foods it imported from Tianyang.

JT and Nissin had planned to buy a scandal-ridden frozen food company in a deal that would have created Japan's biggest frozen food maker.

The methamidophos contamination set off a nationwide scare last week. In addition to the 10 confirmed victims, more than 1,200 people have reported becoming ill after eating Tianyang products, though no link with the pesticide in the additional cases has been proven.

Authorities have ordered the recall of millions of bags of dumplings and other foods made by Tianyang, while many stores and restaurants in Japan have stopped offering Chinese products altogether.

Traces of the insecticide were found in the dumplings, on the packaging and in the vomit of the 10 people who were sickened. The 10 cases involved two separate brands containing similar dumplings.

Investigators in western Japan also found traces of methamidophos on six bags of the dumplings recalled over the weekend.

Punctures were found in a handful of the bags that were recalled or tied to poisonings.

China's product safety agency conducted tests on the ingredients of Tianyang dumplings from the same batch sent to Japan, but found none of the insecticide cited by Japanese authorities.