Japan says it will protect its offshore energy resources after its navy spotted two Chinese destroyers near a disputed gas field in the East China Sea.
A Japanese navy plane located the two destroyers and a supply ship cruising in international waters on Saturday near the gas project 400 km north-west of Japan's southern Kume island, a defence agency spokeswoman said today.
"We cannot say what their motive was, but we want to continue to watch Chinese moves closely," she said. Prime Minister Junichiro Koizumi said Japan would make "utmost efforts to secure our rights over marine resources".
Relations between Japan and China have deteriorated recently. Tokyo lodged a protest last November over the intrusion of a Chinese nuclear submarine near the same gas field.
The mass-circulation Yomiuri Shimbun newspaper reported the destroyers spotted last week were China's most advanced models, equipped with cruise missiles, and it was the first time Japan had found them in the area.
"China is likely to be trying to display its strength in a bid to secure marine resources," the daily quoted an anonymous defence official as saying.
Japan and China are two of the world's biggest energy importers. An initial survey in 1999 estimated the disputed gas field had major reserves of 200 billion cubic metres.
Japan has proposed a border in the field, but China has not recognised the plan. China began drilling in the area in 2003 despite Japanese protests.
In a December blueprint, Japan for the first time told its defence policy makers to regard China as a potential threat.
Outgoing US ambassador to Tokyo Howard Baker said this week that relations with its giant neighbour were the biggest challenge for Japan.