|Japan arrested a Chinese fisherman earlier this month, sending relations with its neighbour into a tailspin [AFP]
Four Japanese nationals have been arrested in China for allegedly filming a military facility, but Japan says it does not see their detentions as part of a simmering diplomatic row.
The four employees of Fujita, a Tokyo-based construction company, had been on a work trip to China's in Hebei province to do research, an executive of the firm said in Tokyo on Friday.
"They were They were bidding for a project to dispose of chemical weapons that were left in China by imperial Japanese forces after World War II, the executive said.
China had told Japan that the four were being held "based on China's laws on the protection of military facilities and on criminal procedure", Yoshito Sengoku, Japan's most senior government spokesman, said. He said Tokyo was trying to get more details through its embassy in China.
China's state-run Xinhua news agency said earlier that the four Japanese men are being investigated for having entered a military zone without authorisation and illegally videotaped military targets.
Fishing boat row
The detentions come as diplomatic relations remain inflamed due to Japan's arrest of a Chinese fisherman earlier this month, with Beijing calling off all high-level official meetings.
China has repeatedly protested and demanded Japan to release the captain of a trawler which Japan suspects intentionally rammed two Japanese coastguard ships in waters near a disputed island chain in the East China Sea.
Japan warned on Friday that the deepening row with China could hurt both of Asia's two biggest
economies and sought to draw a line between a feud over the disputed island and the detainment of four of its nationals.
"I don't think there is any correlation between this issue and the problem surrounding the Senkaku islands", referring to the island chain called Diaoyu by China.
Tokyo and Beijing have agreed that up to 400,000 chemical weapons, left in China as Japan surrendered in World War II, remain in the country, although the exact figure has long been the subject of debate.
Under the United Nations Chemical Weapons Convention, Japan is responsible for cleaning up the weapons. Tokyo has started the process, although technical and diplomatic problems have held up progress.