A Chinese man went on trial Tuesday for poisoning frozen dumplings which sickened 13 people in China and Japan, state media reported, in a case that raised tensions between Beijing and Tokyo.

Factory worker Lu Yueting, 39, was said to have injected insecticide into the dumplings because he was unhappy with his pay and did not get on with his co-workers at the Tianyang Food Plant in the northern province of Hebei.

The contaminated dumplings were sold in Chengde in Hebei as well as being exported to Japan, the state-run Xinhua news agency reported.

Four people fell ill in China and nine in Japan, it said. Earlier reports said 10 people were sickened in Japan, including a small child.

The incident in 2008 raised tensions between Beijing and Tokyo, which often have a difficult relationship, mainly over historical issues and territorial disputes.

Lu's trial at the Shijiazhuang Intermediate People's Court lasted three hours, Xinhua said, and a verdict was to be announced at a later date.

The defendant confessed to the allegations in court, Xinhua reported, adding that he said he felt sorry for the people who became ill.

The agency quoted prosecutors as saying that one person had been made seriously ill while the rest suffered minor illness, and the incident also resulted in significant financial losses.

Lu was accused of "deploying dangerous substances" and Xinhua said a death sentence was possible if his actions were found to have caused "serious injury, death or the loss of property".

He is alleged to have injected insecticide into six to nine boxes of frozen dumplings.

At the time of the incident China initially said the poison was injected into the dumplings after they had reached Japan. When Lu was arrested two years later, Japanese media expressed suspicions about why it had taken authorities so long to do so.

The poisoned dumplings caused Japanese consumers to avoid Chinese frozen food, which temporarily disappeared from stores.

Concerns over Chinese food imports were compounded in late 2008 after six Chinese infants died and almost 300,000 were made ill by milk powder laced with the industrial chemical melamine.