Japan has apologized to China for an accident in which three Chinese people were injured by poison gas that leaked from chemical weapons abandoned by the Japanese army after World War II.

Japan had sent government officials and experts to the southern Chinese city of Guangzhou to check whether the accident had been caused by chemical weapons abandoned by its army.

"Our government truly regrets that the accident happened and expresses our heartfelt sympathy for the sufferers," Japanese Foreign Ministry spokesman Hatsuhisa Takashima said in a statement released late on Sunday.

Takashima said Japan would do its best to quickly scrap all chemical weapons left in China by Japanese forces.

China told Japan that three Chinese citizens were taken to hospital after they inhaled poison gas that leaked from abandoned shells while removing sand on a riverbank in Guangzhou last week, he said.

China has complained that Japan has been slow in clearing up about 2 million chemical weapons buried or discarded by retreating Japanese troops after the war ended in 1945. China says some 2,000 Chinese have been harmed by such weapons.

Japan is required to dispose of chemical weapons left in China by 2007 under an international treaty, the Chemical Weapons Convention. Japanese studies have placed the number of such shells at about 700,000.

In 1999, Japan promised to provide funding, technology, manpower, facilities or other assets needed to scrap the weapons.

In August 2003, a toxic leak killed one man and injured 43 after five canisters of mustard gas were unearthed at a construction site in Qiqihar in the northeastern province of Heilongjiang. Japan has agreed to pay 300 million yen (US$2.75 million) in compensation.

In July 2004, two schoolboys in northeastern China were wounded when they uncovered and played with chemical weapons abandoned by the Japanese army after World War II, according to Chinese media.

Relations between Japan and China have been frayed over a host of issues, at the core of which are disputes that stem from Japan's invasion and occupation of parts of China from 1931 to 1945.

Ties between the two Asian giants have been strained particularly over Japanese Prime Minister Junichiro Koizumi's visits to Yasukuni Shrine, which China sees as a symbol of Japan's past militarism and where convicted WWII war criminals are honored along with Japan's war dead.