China’s Foreign Minister Yang Jiechi (L) attends an ASEAN meeting yesterday in Phnom Penh. Photograph: Heng Chivoan/Phnom Penh Post

Amidst a week of predictable discussion about the South China Sea, a different territorial sea dispute dominated the sidelines of the ASEAN conference in Phnom Penh yesterday.

Japan lodged a protest with China yesterday against the entry of Chinese patrol ships into waters near disputed islands in the East China Sea.

The islands, claimed by Beijing and Tokyo as well as Taipei, are located near rich fishing grounds and potentially huge oil and gas reserves.

In a snap sidelines meet this afternoon, the Chinese and Japanese foreign ministers held off-campus discussions at the InterContinental Hotel.

The Chinese delegation released a statement directly after the meeting emphasising that the disputed islands – known as Senkaku in Japan and Diaoyu in China – and “their affiliated islets have always been China’s territory since ancient times, over which China has indisputable sovereignty”.

The Chinese statement said that Chinese foreign minister Yang Jiechi “urged Japan to adhere to relevant agreements and understanding between the two sides in good faith, return to the right path of managing differences through dialogue and consultation with the Chinese side”.

At a Tokyo press conference, Japanese chief cabinet secretary Osamu Fujimura said: “It is clear that the Senkaku islands are inherently Japanese territory from a historical point of view and in terms of international law and that they are under the effective control of Japan.”

Naoka Saiki, deputy press secretary at the Japanese Ministry of Foreign Affairs, told the Post that the meeting yesterday afternoon between the two foreign ministers had resulted in no resolution at this point.

“Minister of Foreign Affairs Koichiro Gemba lodged a strong protest against Foreign Minister Yang Jiechi of China on this incident,” she said, adding that Gemba also stated the importance of maintaining the bilateral relationships between the two countries.

Under the chairmanship of China’s close ally Cambodia, ASEAN has stipulated that the production of a Code of Conduct for the South China Sea will have Chinese involvement at every step, despite opposition from the Philippines at the ASEAN Summit in April.

In the annual joint communiqué of the foreign ministers in 2011, the 10-member group made it clear that a region code of conduct was an ASEAN-only issue, with “intensive discussion in ASEAN” to follow.

To contact the reporters on this story: Bridget Di Certo at [email protected]

David Boyle at [email protected]

With assistance from Reuters