"A Japanese fact-finding mission has concluded the poison gas accident in Guangzhou city on June 21 was caused by chemical weapons of the former Japanese military," foreign ministry press secretary Hatsuhisa Takashima said.

"The government feels an extreme regret that this kind of accident happened and offers a sincere sympathy for the people injured," he said in a statement late Sunday.

The foreign ministry said Japan had dispatched the mission to the southern Chinese city on Sunday, three days after China notified it of the accident.

The three became ill after inhaling poison gas leaked from abandoned shells while they were collecting sand from a river bank in Guangzhou, the ministry said.

Public broadcaster NHK said they were not in a life-threatening condition.

Japan plans to build chemical weapons recovery and disposal facilities in the Haerbaling district of China's northeastern Jilin province, where most of Japan's abandoned chemical weapons are believed to be buried.

Takashima said Japan "will make utmost efforts ... to dispose of abandoned chemical weapons as soon as possible," adding Tokyo was trying to reach an accord with China early over the Haerbaling facilities.

In August 2003 a Chinese person was killed and 43 others were injured after coming into contact with mustard gas dumped by Japan during the war and dug up at a construction site in Qiqihar city in northeastern Heilongjiang province.

Two schoolboys were similarly hurt in July 2004 after they pried open a bomb containing chemicals in Jilin province.

Japan estimates its forces abandoned more than 700,000 chemical weapons in China during the war, although Chinese experts say as many as two million exist -- the world's largest stockpile of abandoned chemical arms.

Under the UN Chemical Weapons Convention, Japan has until 2007 to destroy all of the chemical weapons its troops left in China.