When Tokyo's nationalist governor suggested buying uninhabited islands at the center of a long-simmering dispute with China, Beijing immediately denounced him and even Japan's government played down the plan, fearing an international firestorm.

Now activists on both sides have put the islands front-and-center in one of the biggest territorial flare-ups between the two Asian giants in years, a collision of the persistent animosities over Japan's imperialist past and the new fears of China's rising economic and military clout.

An unauthorized landing by Japanese activists on a tiny island in what the Japanese call the Senkaku chain — and the Chinese call the Diaoyu — has sparked an outpouring of anger and anti-Japanese protests across China and fueled calls for aggressive government action that some fear could lead to a dangerous escalation of tensions.

Japanese authorities on Monday questioned the 10 Japanese, including Tokyo city assembly members, who swam ashore on the disputed island the day before. News of the landing prompted thousands of Chinese to hold demonstrations in 10 cities, where protesters sang the Chinese national anthem or carried banners demanding Japan give up the islands.

Some vandals targeted Japanese-brand cars.

"Nationalist activists on both sides are working to exploit this issue for their own ends," said Shinji Kojima, a professor emeritus of Chinese history at Tokyo University. "If both governments aren't careful it could lead to a more serious conflict."

The Japan-China tensions are playing out against a backdrop of heightened concern over China's increasingly assertive stance in territorial disputes across the south and east China seas. In July, Beijing announced that a South China Sea military garrison on a remote island was being proclaimed a city, underlining its claims to own the entire, potentially oil-rich region, which is disputed by many of its Southeast Asian neighbors.

Japan's chief Cabinet spokesman, Osamu Fujimura, called this weekend's island landing "regrettable" because it was done without government approval. He also said it was an internal matter and China has no right to complain.

"These islands are our territory," he said.

The landing was the latest in a series of moves by Chinese and Japanese activists since April, when Tokyo's influential governor, Shintaro Ishihara, announced a plan to use public funds to buy several of the isles from a private Japanese citizen whom Japan says has legal ownership.

Within weeks, Tokyo received more than 1 billion yen ($12 million) in donations for the purchase, which is expected to cost between 2 and 3 billion yen.

Ishihara acknowledged the move was largely intended to put pressure on the national government to play a bigger role in the islands' administration. He is now pushing the envelope even further by seeking permission from the central government to send a team of experts there to study development possibilities and environmental issues.

Fujimura on Monday said Japan is considering the proposal, though sending a government-approved mission would likely infuriate Beijing.

The moves by Ishihara have been repeatedly slammed by the Chinese government and media.

Just days before the Japanese group's landing, five Chinese activists went ashore on the island on Aug. 15 — the anniversary of Japan's World War II surrender. The five and nine others were arrested and quickly deported back to Hong Kong.

The islands, also claimed by Taiwan, are important mainly because of their location, which is near key sea lanes. They are surrounded in the East China Sea by rich fishing grounds and as-yet untapped underwater natural resources.

Japan annexed them in 1895, saying no other nation exercised a formal claim. The islands, lying roughly midway between Okinawa and Taiwan, were administered by the United States after World War II until they were returned to Tokyo in 1972.

The conflicting claims have repeatedly flared up in the past, only to quiet down again. Two years ago, relations between China and Japan were soured by the arrest of the captain of a Chinese fishing ship that collided with a Japanese Coast Guard vessel after refusing to leave the region.

By quickly sending the Chinese activists back to Hong Kong, Japan appeared this time to be trying to tamp down the tensions.

In Washington, State Department spokeswoman Victoria Nuland said Monday the U.S. is giving the two governments the same message privately that it is giving publicly: that they need to work out the dispute through consultation, not through provocation.

China already is at loggerheads with other Asian nations in island disputes.

The Philippines, which claims South China Sea islands close to its main shores, has described as unacceptable Beijing's move last month to establish its new city on a remote island in the sea some 350 kilometers (220 miles) from China's southernmost province. Vietnam called China's move a violation of international law.

The United States, which maintains a large naval presence in the Pacific, has said maintaining freedom of navigation in the sea is in its national interest, a position that has angered China.

The latest tensions come as China's ruling Communist Party prepares for a major leadership transition and leaders in both China and Japan face strong domestic pressure to make a show of get-tough positions on matters of national territory.

Appealing to anti-Japanese sentiment, which is still strong in the countries that suffered under Japan's pre-1945 imperialism, is also often seen as a good way to elicit nationalist support in China and North and South Korea.

Earlier this month, South Korean President Lee Myung-bak visited a disputed island in the Sea of Japan, called Takeshima in Japanese and Dokdo in Korean, that was widely seen as an attempt to play up such sentiment ahead of elections later this year.


AP reporters Scott McDonald in Beijing, Emily Wang on Ishigaki Island, Malcolm Foster in Tokyo and Matthew Pennington in Washington contributed to this story.