Japan's military yesterday shadowed an unidentified submarine that entered its territorial waters the day before, but officials said they had not yet figured out what country the intruder was from.
Tokyo put its navy on alert on Wednesday after spotting the submarine off Okinawa, and sent a reconnaissance plane and destroyer to follow its movements.
The sub, which spent two hours in Japanese waters before leaving, was heading north yesterday, Chief Cabinet Secretary Hiroyuki Hosoda told a news conference.
He refused to confirm media reports that defense officials believe the vessel is from China, saying: ``We don't have enough conclusive evidence to make a determination.''
He said it would take some time to identify the submarine because it hasn't surfaced and didn't appear to be heading toward a specific country. Hosoda said Tokyo hasn't confronted any countries about the incident.
Judging from its cruising sound, however, the Defense Agency believed the vessel to be a Chinese navy Han-type nuclear submarine, Japan's mass-circulation Yomiuri Shimbun and Jiji Press news agency said.
The Japanese navy has been trailing the submarine with two destroyers and a surveillance airplane, a defense agency spokesman said.
Officials have refused to confirm media reports that Tokyo was investigating a possible link between the sub sighting and China's recent exploration of natural gas fields in Japan's southern waters.
Yomiuri said defense officials suspect Beijing may have sent the vessel to head off criticism from Tokyo about China's recent surveys for gas fields near Okinawa.
Territorial disputes have occasionally flared up between Japan, China and South Korea, including one that has deepened in recent months with Beijing over natural gas deposits in the East China Sea.
Tokyo has accused China of conducting surveys for gas fields near Okinawa that extend into Japanese territorial waters. China says its activities are close to its coast and don't concern Japan and has rejected offering more details.
Meanwhile, China yesterday said it knew nothing about a submarine that entered Japanese waters near a disputed gas field and sparked a high seas chase.
"We don't know. We are not aware of this situation," the foreign ministry said in China's first response to the incident.
While the Xinhua news agency ran a brief report from Tokyo about the unidentified sub on Wednesday, it has filed nothing since and the story failed to appear in any major state-run media yesterday.