Chinese protesters gather outside the Japanese Embassy in Beijing on Tuesday. Chinese government ships are patrolling near contested East China Sea islands in a show of anger after Japan moved to assert its control in the area. (Ng Han Guan/AP)

China on Tuesday sent two patrol ships to waters near a remote and disputed island chain in a show of its “undisputable sovereignty,” Chinese state media said, escalating a territorial showdown between Asia’s two largest economies.

The move came as a direct response to Japan’s nationalization of the uninhabited islands, finalized Tuesday when the central government’s cabinet approved a $26.2 million purchase of the land from a private Japanese owner.

“We are watching closely the evolution of the situation and reserve the right to take reciprocal measures,” said Geng Yansheng, a Chinese Defense Ministry spokesman, according to Beijing’s state-run Xinhua News Agency.

Japanese government officials have made the case that the purchase should do little to fray ties with Beijing; Japan’s government previously rented the land and tightly controlled it, allowing landing permission to almost nobody.

The purchase, one government spokesman said Tuesday, will ensure “stable peace and maintenance” of the land, which is also claimed by Taiwan. The uninhabited islands are significant because they occupy precious shipping lanes and may contain oil deposits.

“It’s important to avoid any misunderstanding by the Chinese government,” said the spokesman, Chief Cabinet Secretary Osamu Fujimura.

But China has reacted with fury, and the two countries, which both view the islands as a symbol of nationalist pride, have pushed each other to a tense standoff — one that raises the potential for small-scale armed conflict, some security experts say.

To counter the Chinese ships, Japan sent a coast guard patrol vessel to the area, Japan’s Asahi Shimbun newspaper reported.

U.S. State Department spokeswoman Victoria Nuland on Tuesday said the United States’ position on the dispute remains “that we want to see China and Japan work this through.”

A Xinhua editorial called Japan’s decision to nationalize the islands “ridiculous and absurd” and an “open provocation against China.” Sending the patrol ships from China Marine Surveillance — one of 11 loosely regulated agencies or paramilitary groups China has used in its increasingly aggressive push for control of the East China and South China seas, according to a recent report from the Brussels-based International Crisis Group — “is timely and necessary,” the editorial continued. “The action dealt a big blow to the inflated swagger of Japan.”

The report from Brussels said the marine surveillance unit “enjoys considerable independence outside the government’s power structure” and has been involved in clashes with Philippine and Vietnamese ships.

Japan and China have conflicting narratives about the history of the islands, known in Japanese as Senkaku and Chinese as Diaoyu. Japan, which has controlled the rocky outcroppings for four decades, says China showed interest in the territory only after studies suggested a bounty of natural resources in the nearby waters. Beijing, meanwhile, says the land has been China’s since “ancient times,” discovered and named by Chinese people and appearing on Chinese maps drafted centuries ago.

“China will take any necessary measures to uphold its national territorial sovereignty,” Hong Lei, China’s Foreign Ministry spokesman, said during a regular news briefing Tuesday. “We demand that the Japanese let go of its wrong actions and come back to the negotiating table to resolve the Diaoyu islands issue.”

The low-simmering territorial dispute began to boil in April, when Tokyo’s nationalist governor, Shintaro Ishihara, told a think tank in Washington of his city’s plan to nationalize the islands. Japan’s central government, fearing that Ishihara would directly confront China if he bought the land, decided to launch its own bid — a move designed to decrease tensions, not raise them.

But China’s Foreign Ministry on Monday denounced the purchase as a “gross violation” of Chinese sovereignty. Premier Wen Jiabao told university students in Beijing that China “will never budge, even half an inch, over the sovereignty and territorial issue.”

Many Chinese citizens view Japan’s claim to Diaoyu as a land grab akin to the country’s brutal invasion of China before and during World War II. The wounds from that war are still raw for some. Just this week, five Chinese citizens sued the Japanese government for bombing Chongqing between 1930 and 1944, demanding a worldwide apology from Japan.

On Tuesday afternoon, about 50 young protesters gathered in front of the Japanese Embassy in Beijing, pumping their fists at the front door and chanting that Japan was illegally claiming the contested islands.

“Diaoyu has always been China’s,” said Li Jie, one of the protesters. “If the [Chinese] government wants to go to war, I’ll join the military.”

There have been other land-based flare-ups in the past several years but perhaps none as tense as this one. It comes as China’s profile in the world is rising steadily and Japan’s diminishes. Nationalists in Japan have seized on this sense of insecurity to wage their claims on the islands.

Both China and Japan have signed the U.N. Convention on the Law of Sea, which says that countries control territory within 12 nautical miles from their coastline and have exclusive economic rights within 200 nautical miles of their coastline. The islands Japan has purchased are 200 nautical miles from both China and Japan. China on Monday released a detailed list of latitudes and longitudes marking its definition of its boundaries — a sign to some observers that the dispute is escalating.

Japanese Prime Minister Yoshihiko Noda has said Japan’s remote islands are essential for marking the country’s “exclusive economic zone.” Japan is the 61st-largest country in the world according to land mass, Noda said, but the sixth-largest based on the size of the ocean it manages.

“What makes Japan such an expansive maritime nation is our over 6,800 remote islands, including Takeshima and the Senkaku Islands,” Noda said.

South Korea also claims Takeshima.

“We’d never see a total war” between China and Japan, said Yuichi Hosoya, a professor of international politics at Keio University in Tokyo. “But we could see a small-scale conflict. We saw a clash in 2010” — when Japanese and Chinese boats collided and Japan detained a Chinese fishing captain — “and we will possibly see a harsher clash soon.”

Yang reported from Beijing. Liu Liu in Beijing contributed to this report.