A territorial flare-up between China and Japan has intensified as two Beijing-sent patrol ships arrived near disputed East China Sea islands in a show of anger over Tokyo's purchase of the largely barren outcroppings from their private owners.

The China Marine Surveillance has drawn up a plan to safeguard China's sovereignty of the islands and the ships were sent to assert those claims, said the Chinese government's official news agency, Xinhua. The marine agency is a paramilitary force whose ships are often lightly armed.

The rocky islands, known as Senkaku to Japanese and Diaoyu to Chinese, have been the focus of recurring spats between the countries and also are claimed by Taiwan. The China-Japan dispute has been heating up in recent months, in part because the nationalist governor of Tokyo had proposed buying the islands and developing them.

Japan's central government announced its own deal this week with the Japanese family it recognizes as the owner. Chief Cabinet Secretary Osamu Fujimura told reporters the government budgeted 2.05 billion yen ($26 million) for the purchase "to maintain the Senkakus peacefully and stably."

Public broadcaster NHK said the government and the family signed a deal Tuesday.

The government does not plan to develop the islands. Several experts interpreted the move as an attempt to block the plan by Tokyo governor Shintaro Ishihara, which could have raised tensions further. Ishihara also had said he hoped to visit the islands in October.

"Ishihara put the national government in a very difficult spot. He pushed them into doing this now," said Sheila Smith, a senior fellow at the Council on Foreign Relations in Washington. But she said this was a "good outcome" that should be seen as an attempt by Tokyo to sideline Ishihara.

Japan cannot afford to let the dispute hinder its vital ties with China, its top trading partner, she said.

East Asian neighbours are critical to "Japan's future in a substantive way," Smith said. Tokyo needs to be able to work through "different problems with Beijing in order to make sure the economic interdependence between those two countries continues to serve both nations' needs."

Anger in China

Beijing, however, responded with fury, with Premier Wen Jiabao among those warning that China would never back off its claims.

China's Foreign Ministry said Monday in a statement, "If Japan insists on going its own way, it will bear all the serious consequences that follow."

Japan has claimed the islands since 1895. The U.S. took jurisdiction after the Second World War but turned them over to Japan in 1972. But Beijing sees the purchase as an affront to its claims and its past calls for negotiations.

Carlyle Thayer, an expert on regional security at the University of New South Wales in Australia, said China's sending of the patrol boats "ups the stakes."

"It's a tit-for-tat response because China is extremely sensitive about sovereignty matters," he said. "What is possible are the kinds of confrontations like occurred at Scarborough Shoal," a disputed reef where Chinese and Filipino boats faced off earlier this year.

"It's all posturing. It's a game of who blinks first," said Thayer.

Japan's coast guard said it has not taken any special measures in response to the Chinese patrol boats although it continues to monitor the situation.

Chinese media fuel dispute

Beijing's anger has been accompanied by heated reporting in China's state media. The tabloid Beijing Morning Post ran a full-page colour photo of one of the islands with the headline: The Diaoyu Islands China's Territory.

China on Tuesday also started broadcasting a daily marine weather report for the islands.

About a dozen protesters gathered outside the Japanese Embassy in Beijing, chanting, "Japan, get out of China." A car drove slowly toward the embassy's well-guarded gate but did not make a serious attempt to ram it and was stopped by uniformed and plainclothes police.

Taiwan's Foreign Ministry also lodged a strong protest to Japan. In a statement it called the island purchase an "extremely unfriendly move" that "not only harms the longtime co-operation between Taiwan and Japan but will also aggravate regional tensions in East Asia."

Top Japanese government officials maintain that the flare-up hasn't affected official ties with China, although Deputy Prime Minister Katsuya Okada acknowledged that emotions on both sides were being fanned by activists.

Prime Minister Yoshihiko Noda met only briefly with Chinese President Hu Jintao on the sidelines of this past weekend's Asia-Pacific Economic Co-operation summit in Vladivostok, Russia, and Japanese news reports said Noda emphasized the importance of dealing with the island dispute from a broad perspective. Noda also said that "China's growth is a chance for the world and we would like to develop it in a strategic manner."

China also has announced co-ordinates marking out the waters off the Diaoyu Islands that it considers its territory, apparently for the first time after doing so earlier for the mainland and other islands.

The co-ordinates are another step, along with recent announcements of China's intention to use law enforcement vessels, to defend its sovereignty claim, said Stephanie Kleine-Ahlbrandt, northeast Asia project director for the International Crisis Group.

"It's primarily about being seen as taking action to pave the way for further actions to assert China's sovereignty," she said.

In Tokyo, Gov. Ishihara renewed his calls for the islands to be developed for future use by fishermen.

"It appears that the matter is decided," he told reporters. "They say they won't do anything, but China's leaders are still criticizing the plan."

Ishihara said he was freezing the 1.4 billion yen ($18 million) donated toward his purchase plan for the islands and would only release the funds to the government once it was clear whether a port or other facilities would be built.

He also suggested that Japan unite with the Philippines and Vietnam, which have disputes with China in the South China Sea.

"We shouldn't see this as an issue that only concerns Japan," he said.