China said on Friday it had every right to drill in the East China Sea close to waters disputed with Japan, adding that it did not recognise a “unilateral” Japanese median line setting out a boundary between the two in the waters.

Japan this week called on China to halt construction of oil-and-gas exploration platforms in the East China Sea close to waters claimed by both nations, concerned that Chinese drills could tap reservoirs that extend into Japanese territory.

Patrol ships and aircraft from both countries have been shadowing each other in the area over the past couple of years, raising fears of a confrontation and clash.

In an escalation of the latest dispute, Japan released aerial photographs of China’s construction in the area, accusing it of unilateral development and a halfhearted attitude towards a 2008 agreement to jointly develop resources there.

China resumed exploration in the East China Sea two years ago, Japan said. In 2012, Japan’s government angered China by buying a disputed island chain there from private owners.

A group of disputed islands, Uotsuri island (top), Minamikojima (bottom) and Kitakojima, known as Senkaku in Japan and Diaoyu in China is seen in the East China Sea, in this photo taken by Kyodo September 2012. Photo: Reuters/Kyodo

Before then, China had curtailed activities under an agreement with Japan to jointly develop undersea resources in disputed areas.

The platforms are being erected on the Chinese side of a median line delineating the exclusive economic zones of the two countries, according to a Japanese ministry official.

China’s Foreign Ministry said its drilling activities in waters which are not disputed and under Chinese administration are “completely appropriate and legal”.

“China and Japan have not yet delineated maritime boundaries in the East China Sea, and China does not recognise the Japanese side’s unilateral marking out of a so-called ‘median line’,” the ministry said in a statement.

China’s position is that it had a 200 nautical mile exclusive economic zone, and its continental shelf in the East China Sea extends to the Okinawa Trough, it added.

In a separate statement, China’s Foreign Ministry said that it was “extremely concerned” Japan had allowed a visit by former Taiwan president Lee Teng-hui, a man despised by Beijing for asserting the self-ruled island’s sovereignty.

“Lee Teng-hui is a stubborn Taiwan splittist. The Japanese side ignored China’s stern representations and provided convenience for him to visit Japan and engage in Taiwan separatist activities,” it said.

China claims self-ruled Taiwan as its own and has never renounced the use of force to bring it under its control.

Reporting by Ben Blanchard; Editing by Robert Birsel.