The Japanese government deliberately continued with its illegal actions of "buying" China's Diaoyu Islands on Tuesday despite a string of strong warnings and opposition voiced by top Chinese leaders.

The Japanese government signed on Tuesday a contract with the Kurihara family, who are claimed by the Japanese side as the "private owner" of the Diaoyu Islands, Japan's NHK television reported.

The signing of the contract came shortly after the Japanese cabinet's decision earlier in the day to disburse reserve funds to "purchase" part of the islands, local media reported.

Japan's Chief Cabinet Secretary Osamu Fujimura announced Monday afternoon that the central government reached the final agreement with the Kurihara family to buy three of the five uninhabited islands.

The purchase will cost the Japanese government some 2.05 billion yen ($26.15 million).

Demonstrating China's undisputable sovereignty over the islands, two ships of the China Marine Surveillance (CMS) reached the waters around the islets Tuesday morning.

The CMS has drafted an action plan for safeguarding the sovereignty and would take actions pending the development of the situation, the CMS sources said.

On Monday, China's foreign ministry promptly challenged Japan's reckless action over the Diaoyu Islands. Chinese Foreign Ministry spokesman Hong Lei said China firmly opposes the move.

Meanwhile, Chinese Foreign Minister Yang Jiechi on Monday urgently summoned Japanese Ambassador to China Uichiro Niwa for a meeting to lodge solemn representations and strong protest against the Japanese government's illegal "buying" of the islands.

Yang said the Diaoyu Islands and their affiliated islets have been inherent territory of China since ancient times, backed by historical and legal evidence. The Japanese government's so-called "purchase" of the islands and other unilateral actions are illegal and invalid.

China urges Japan to immediately revoke its wrong decision and stop all actions that undermine China's territorial sovereignty. Otherwise, all consequences should be borne only by the Japanese side, Yang said.

As a countermeasure, the Chinese government announced the base points and baselines of the territorial waters of the Diaoyu Islands, which is in accordance with China's law on territorial seas and adjacent zones adopted in 1992.

Also on Monday, Chinese Premier Wen Jiabao said the Diaoyu Islands are an inalienable part of China's territory and China will "absolutely make no concession" on issues concerning its sovereignty and territorial integrity.

Wen made the remarks while addressing an inauguration ceremony for a statue of late Chinese leaders Zhou Enlai and Chen Yi at the China Foreign Affairs University in Beijing.

"The Chinese government and its people cherish their country's hard-won national sovereignty and dignity more than anybody," Wen told the students, noting that China has maintained such a firm and unyielding character even in situations of extreme hardship.H Additionally, while meeting with Iranian Parliament Speaker Ali Larijani in Tehran on Monday, visiting Chinese top legislator Wu Bangguo also made strong opposition, and reiterated China's position on the issue.

These strong protests from the China's top leadership came after President Hu Jintao's face-to-face talks with Japanese Prime Minister Yoshihiko Noda on Sunday on the sidelines of the annual meeting of the Asia Pacific Economic Cooperation forum in Russia's Vladivostok.

The top Chinese leader pointed out that China-Japan relations have recently faced a severe situation due to the Diaoyu Islands issue, adding that whatever ways the Japanese side uses to "purchase the islands" are illegal and invalid and China firmly opposes such moves.

Hu said that Japan must fully recognize the gravity of the situation and should not make wrong decisions. He urged Japan to work with the Chinese side to maintain the overall development of the two countries' relations.

The Diaoyu islands, in the East China Sea between China and Japan, have belonged to China since ancient times. For centuries, fishermen from China's Taiwan and Fujian and other provinces conducted activities such as fishing and collecting herbs in the area.

The islands appeared on China's map since the Ming Dynasty (1368-1644). There are records about the islands in a book published during the rule of Yong Le (1403 to 1424) in the Ming Dynasty, more than 400 years before Japan claimed discovery of the Diaoyu islands in 1884.