China lodged a strong protest with Japan on Friday over what it called an infringement of its sovereignty and interests in the East China Sea after Tokyo granted rights to test-drill for gas in disputed waters.
The official Xinhua news agency said the head of the Foreign Ministry's Asia department had summoned a minister from the Japanese embassy "to lodge solemn representations to and express strong protest" against the decision.
"This action by Japan is a serious provocation to, and infringement on, China's sovereign rights and interests," Cui Tiankai was quoted as saying.
He said it also violated the UN Convention on the Law of the Sea and called on Japan to "correct its decision and stop any action that impairs China's sovereign rights and interests".
Despite China's ire, a Japanese government spokesman said the issue would not harm relations.
In recent months ties between China and Japan have been at their worst since diplomatic ties were established in 1972.
Several disputes have flared up, among them Tokyo's bid for a seat on the UN Security Council and Japanese Prime Minister Junichiro Koizumi's visits to a shrine where convicted war criminals are honoured alongside Japan's 2.5 million war dead.
Japanese energy exploration firm Teikoku Oil Co said on Thursday it had been awarded rights to begin test-drilling in a natural gas field near a sector of the East China Sea disputed by Tokyo and Beijing.
Japan and China, which both rely heavily on energy imports and are anxious to secure new energy sources, have been at odds over China's exploration for natural gas near areas that Japan claims as being within its own exclusive economic zone.
Teikoku was the first Japanese firm to apply after the government said in April that it would start processing applications for East China Sea drilling rights.
Japan considers waters east of the midway point between its coastline and that of China to be its exclusive economic zone, but China does not recognise the line.
"The views of the two parties on the issue of setting the boundary in the East China Sea differ, and we cannot accept China's position," Hiroyuki Hosoda, Japan's top government spokesman, told a news conference.