Japanese scientists fired mustard gas at Chinese prisoners of war and forced them to drink liquid forms of the poison in a World War II chemical weapons experiment, a researcher said on Saturday.

Yuki Tanaka, a lecturer at the Center for Asian Studies at the University of Adelaide, South Australia, said Japan's involvement with chemical weapons began in 1918 and culminated with a manufacturing complex on Okunoshima, a tiny island in the inland sea."Only parts of this story have been told before," he said in an article in the October issue of the Chicago-based Bulletin of the Atomic Scientists.

"In September, 1985, the Japanese journal Sekai described the actual use of chemical weapons by the Imperial Army against China. But until now only the people living in the immediate area where the weapons were once produced have been aware of the details of the production and its effects on workers," he wrote.

Tanaka said his article, which details the health effects on people, including schoolchildren, who worked at the chemical complex, was an attempt to confront the "stubborn silence" of the Japanese government, which refuses to talk about the chemical weapons program.

He said previously published reports indicated that 2,000 Chinese were killed and 35,000 injured by Japanese chemical weapons after Japan invaded China at the dawn of World War II.

Tanaka cited a diary from one military unit which said 16 Chinese prisoners were forced to undergo an attack by 9,800 mustard gas shells over a four-day period in 1940. Some of the prisoners were allowed gas masks while others were not. They were dressed in differing kinds of clothing and positioned in both sheltered and unsheltered locations in the test area.

The diary records headache, fatigue, blisters, skin discoloration, constant tears, pain and other symptoms.

In another experiment five prisoners, some of whom had earlier been exposed to the gas, were made to drink a liquid form of the agent.

He said the island was erased from war-era maps and eventually employed 5,000 to 6,000 people, including many schoolchildren, toward the end of the war.