Scientists believe they have located the site of a toxic gas experiment plant probably the largest in the world built by the occupying Japanese army in Inner Mongolia.

It has long been recognized that the Japanese used Chinese people as human guinea pigs to develop poison gas in preparation for a planned invasion of the Soviet Union in the early stages of WWII.

Now Chinese scientists say they have found one of the test sites. Deep in the heart of the grasslands around Bayanhan, Hulun Buir city, the site covers an area of more than 100 square kilometers, according to Xu Zhanjiang, a researcher on the history of Japanese germ warfare with the Harbin Municipal Academy of Social Sciences in northeast China's Heilongjiang Province.

The discovery is the result of a research program begun in 2000 by the academy to explore Japanese war crimes during the 1930 and 40s.

A clue to the existence of the plant came from the memoirs of some Japanese soldiers, in which they mentioned some cruel and inhuman gas experiments they had been party to in the region, said Xu.

After five years of investigations and piecing together evidence collected from elderly locals in the autonomous region, researchers finally homed in on one particular area.

Many pits, the size of which vary from 10 to 30 square meters, are visible on the grasslands.

Several hundred such sites have remained undisturbed in the Banyanhan plant which researchers say extends to an area about 9 kilometers wide and 13 kilometers long.

As the plant was concealed deep in the grasslands where few people ventured and thanks to the good vegetation, it has escaped human interference and remained well-preserved for more than 60 years.

"It may be the largest scale and best preserved gas experiment site in the world," said Xu.

More than 20 different sites, such as trenches, shelter for vehicles and tanks, a communication centre and experiment pits, have been found.

One local, Adebi, born in the 1920s, recalled hearing from a friend that the Japanese were conducting gas bomb experiments on live humans deep inside the grasslands.

"Many herders could often smell an irritating odour wafting over the grasslands in 1941 and many people and animals began to be infected by plague," Xinhua News Agency quoted him as saying.

Xu said that there were two reasons why the Japanese forces had built the gas plant in Bayanhan.

One is that the place is sparsely populated, making it easier to cover up such atrocities. The other is that Japanese forces had, at that time, intended to attack the USSR whose climate and natural conditions, in many regions, are similar.

Further investigations, which include searching for gas bomb shrapnel and contaminated soil samples, is still to be done.

"This is an important part of the Japanese invasion of China and also strong evidence of the germ warfare they conducted here," Bao Haichun, head of the academy, told the Beijing-based International Herald Leader newspaper under Xinhua.

(China Daily July 4, 2005)