Li Guizhen suffered horrific injuries after coming into contact with the gas earlier this month and died Thursday at the No. 203 Hospital of the Chinese People's Liberation Army in Qiqihar city, in northeast China's Heilongjiang province, the Xinhua news agency said.

Five containers of the lethal gas, sealed with lead and wrapped in plastic, were uncovered on a construction site in Qiqihar on August 4.

One was accidentally broken, causing an oil-like substance to leak in surrounding, poisoning at least 41 people.

It was later confirmed to be mustard gas, which Tokyo admitted was buried by its army nearly 60 years ago.

The risk of poisoning increased because contaminated soil was removed to several different places in the city, and doctors at the hospital have warned more victims could emerge as symptoms can take up to one month to appear.

China lodged a formal protest about the incident with Japan, which has since removed the containers.

"The government of Japan expresses its heartfelt condolences to the family of the victim who passed away," Japan's ministry of foreign affairs said in a statement Friday.

"To prevent another such tragedy, the government of Japan intends to deal appropriately with the case, in accordance with the Chemical Weapons Convention, to dispose of the dangerous chemical weapons as soon as possible.

"The government of Japan will also continue to respond sincerely to the accident in close cooperation with the Chinese side," it said.

Li's distraught father, who donated his son's body to the hospital for medical research, demanded that Tokyo pay for its actions.

Li Guoxiong said he wanted Japan to compensate him in seven ways, Xinhua quoted him as saying.

This would include fees for supporting his son's wife and parents from both sides, rearing his son's children, interrupting to work, mental distress, burial, and transportation of his son's relatives to the funeral.

Li was a farmer from central China's Henan province who made his living by collecting and selling discarded materials.

Qiqihar, which was occupied by the Imperial Japanese Army for 14 years, still uncovers ghastly reminders of the war on a regular basis.

Since 2001, a total of 775 bombs and artillery shells and 28 gas containers have been discovered in the city.

It is estimated that more than 700,000 chemical weapons were abandoned throughout China by Japanese soldiers in the closing months of World War II.

Japan's brutal occupation of Chinese territory before and during the war remains a source of tension between the countries.

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