JAPAN and South Korea, allies of the United States since World War II, are supposed to be part of an Asia-Pacific counterbalance to China's growing power and its expansive maritime and island claims in East Asia's seas.

Instead, as the region marked the anniversary last week of the end of a war that devastated the region, an upwelling of nationalism showed how fragile reconciliation is, decades after the fighting ended with Japan's surrender to US and allied forces.

Today, it seems that ultra- nationalism among the leading local contestants in North-east Asia - China, Japan and South Korea - is gaining strength, raising the risk of armed conflict.

The rhetoric was certainly strident as China demanded that Japan immediately and unconditionally release 14 activists who had sailed from Hong Kong and landed on the disputed Senkaku Islands in the East China Sea.

Japan had no sooner deported the 14 when tension with China was raised again over the weekend after a group of Japanese nationalists landed on the Senkakus, called Diaoyu in China, despite an official ban.

Japan administers the uninhabited islands in the teeth of opposition from China and Taiwan. Beijing says they belong to China.

The Global Times, part of a newspaper chain published by the ruling Communist Party, said that Japan now has to make a choice: "Create conditions to reduce tensions over Diaoyu, or head into a full confrontation with China. Whatever Japan's choice, China will respond accordingly."

Renewed tension with China came just days after South Korea's President Lee Myung Bak inflamed another offshore dispute when he became the first South Korean leader to land on the rocky Dokdo islets in the sea between South Korea and Japan.

The latter claims ownership of the islets, calling them Takeshima, even though they are garrisoned by South Korea. In response to Mr Lee's visit, Japan recalled its ambassador to South Korea and cancelled a planned meeting of the two countries' finance ministers.

Both China and South Korea also used the anniversary of the end of WWII in Asia to protest against the visit by two Japanese government ministers to a shrine commemorating Japanese who died in the fighting and its aftermath, including 14 convicted war criminals. In separate statements, Seoul and Beijing called on Japan to fully atone for its brutal occupation of parts of China before and during the war, and for its colonisation of Korea in 1910 to 1945.

These issues have flared up before, but never in unison and amid a cascade of tension. What accounts for the surge of vitriol?

Politics has a lot to do with it. China, Japan and South Korea are all facing critical elections later this year. Defending offshore claims strongly in the name of national pride and integrity is seen as a way to seek re-election or the appointment of candidates approved by outgoing incumbents.

If this analysis is correct, it holds out hope that calmer seas will prevail once the politicking season is over.

Yet jingoism cannot be airbrushed away. It is strongly entrenched in both China and South Korea, where tapping anti-Japanese sentiment guarantees public support. In Japan, where pacifism has prevailed since 1945, close observers are warning of virulent nationalism gaining a stronger foothold as the views of previously marginal right-wing politicians converge with those of younger lawmakers and voters concerned about Japan's economic future and its eclipse by China.

Ms Sheila Smith, a Japan specialist at the Council on Foreign Relations in New York, has just returned from several weeks in Japan. She believes that the last serious clash over the Senkakus in 2010, after a Chinese fishing trawler rammed two Japan Coast Guard vessels, transformed Japanese thinking about the defence of its offshore islands.

She says it stimulated for the first time a serious popular response that will make it more difficult to contain and manage tensions with China over the Senkakus in future.

Underlying the nationalism is an intensifying struggle for resource control and strategic advantage between China and Japan, the world's second and third largest economies respectively.

The Senkakus offer access to rich fisheries and potentially valuable seabed resources, including oil and natural gas.

They are part of Japan's prefecture of Okinawa, a sparsely populated island chain. Key US bases there help Japan contain the expansion of Chinese naval power in the Pacific. The main island, Okinawa, is the hub of US airpower in the region.

The Global Times last month called on the Chinese government to consider challenging Japan's rights to Okinawa prefecture on the grounds that it became officially part of Japan only in 1879 after centuries of paying tribute to Chinese emperors.

The US returned Okinawa, including the Senkakus, to the administrative control of the Japanese government in 1972.

Just last month, Japan's Kyodo news agency reported from Washington that a senior State Department official, whom it did not identify, had reaffirmed that the US would be obliged to consider military intervention in support of its ally if Japanese forces defending the Senkakus came under foreign attack.

Against this background, China is unlikely to risk taking the Senkakus by force in the immediate future. Instead, it will maintain its claim, build its strength and keep challenging Japan's control.

The writer is a visiting senior research fellow at the Institute of Southeast Asian Studies.