The poisoning incident of Chinese dumplings exported to Japan was a special case of sabotage and it is unlikely to have happened in China, said China's security and quality watchdogs on Thursday.

"After comprehensive investigation, we believe there's little chance that methamidophos was put into dumplings in China," said Yu Xinmin, the Ministry of Public Security (MPS) criminal investigation bureau deputy director, at a press conference.

The General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ), China's quality watchdog, told the media it came to the same conclusion after finding no harmful chemicals in relative products and samples and no abnormal operations on the part of the Chinese producer.

"We conclude that the dumpling poisoning incident is an individual contrived case instead of a case of food safety resulting from pesticide residue," said Wei Chuanzhong, AQSIQ deputy chief.

In January, Japanese media reported 10 people fell ill in the country after consuming frozen meat dumplings that were found to contain methamidohpos. They were produced by Tianyang Food Plant based in north China's Hebei Province.

Experiments show methamidohpos can penetrate into sealed packages from the outside, said Wang Guiqiang, an expert of evidence authentication with the ministry.

The Japanese police argued it's unlikely the sabotage happened in Japan. They said they concluded the opposite results of similar experiments and found impurities in the methamidohpos, which showed the substance was not produced in Japan.

"Our tests can better reflect the real situation as our choice of materials and design are closer to realities," Wang said.