Nevertheless, three Chinese warships passed through the Osumi Strait, between southern Kyushu and the island of Tanegashima, on Sunday. The vessels, identified as two frigates and an intelligence-gathering ship, were located by a Japan Maritime Self-Defence Force patrol aircraft about 430 kilometres west of the island of Yakushima.

'And I would be surprised if the warships that passed close to Kyushu had done so without some sort of coordination with the authorities that are responsible for the UN territorial discussions,' Okamoto said. 'They are serving notice on what they think of this momentous decision on maritime boundaries by the UN commission.' The vessels were operating within international law, Japan's Defence Ministry said, although it was the first time in nine years that Chinese warships had passed through the strait.

Analysts say the timing of the fleet's voyage is no coincidence, with some accusing Beijing of applying 'gun-boat diplomacy' to its territorial disputes with Japan.

It came on the day when Japan's Prime Minister Yoshihiko Noda left for talks in Washington with US President Barack Obama. As expected, China's increasing military build-up was the main topic on the two leaders' agenda and a statement released after their meeting agreed on what was termed a 'new vision' for the Japan-US alliance that will help to shape the Asia-Pacific region 'for decades to come' - and a thinly veiled reference to efforts to keep an increasingly aggressive and territorially demanding China in check.

It also came less than one day after officials in Tokyo announced that the United Nations Commission on the Limits of the Continental Shelf had approved the addition of 310,000 square kilometres to Japan's continental shelf, effectively granting Tokyo sovereignty over a vast area of the Pacific that is believed to hold vast deposits of natural resources.

'It's nothing less than gunboat diplomacy by China,' said Yoichi Shimada, a professor at Fukui Prefectural University.

He also accused the Chinese government of 'hypocrisy' in its approach to maritime disputes, pointing out that it insists on applying the median line as the determining factor in disputes over territory with other nations, such as Vietnam and the Philippines, but relying on the continental shelf argument when that measurement of a nation's territory is in its favour.

'China does not have a legitimate argument in any of these maritime disputes and all they understand is the application of brute force,' he said. 'It is important that Japan and the US stand shoulder to shoulder against China on this issue.'

He said other nations embroiled in similar disputes should also unite to stand up to China.

'The key will be for all the nations involved to stand firm and be unwavering,' he said. 'The lesson that we should learn from our experiences in 2009, when a Chinese fishing boat clashed with the Japanese coastguard off the Senkakus, is that if you do not soften your position, then China will cave in.'

And in the wake of the recent increase in activities by Chinese warships in waters close to Japan, Shimada said the Japanese military should respond in kind. 'The Self-Defence Force should execute the same kind of exercises, regardless of any reactions from China,' he said. 'It is clear that it is useless to ask Beijing to refrain from its behaviour, so we should conduct exercises even if they are seen by China as aggressive.'

Beijing was quick to dismiss the claim by Tokyo that the UN commission had supported its claim on the extension of the continental shelf, particularly in waters close to Okinotori Island.

In a press conference in Tokyo on Saturday, Foreign Ministry spokesman Liu Weimin said the commission's decision had not been announced.

'I do not know on what grounds Japan made such a claim,' Liu said, repeating Beijing's assertion that the atoll - which is 1,700 kilometres south of Tokyo and covers a mere 10 square metres at high tide - cannot sustain human habitation and therefore should not be used to extend Japan's exclusive economic zone or its continental shelf.

South Korea voiced similar opposition to the application, which was first filed in November 2008, comprising seven maritime areas to the south and southeast of Japan's main islands.

Tetsuya Yoshimoto, deputy director of the Ocean Division's International Legal Affairs Bureau of the Ministry of Foreign Affairs, said it was still considering the decision, which postponed a final ruling on the Southern Kyushu-Palau Ridge region.

Palau has raised no objections to the Japanese application, but China's position on Okinotori means that discussions would have to continue, Yoshimoto said. 'We will continue to make the utmost efforts to ask the commission to make a recommendation on that area,' he said. '