The foreign ministry pledged on Wednesday to take "necessary measures" to defend the country's territorial sovereignty after reports said the Japanese government has reached a deal with a local family to purchase the Diaoyu Islands.

Citing unidentified government sources, the Kyodo News Agency reported early Wednesday that the Japanese central government has reached an agreement with the Kurihara family, which claims to own the Diaoyu Islands, to buy the islands for 2.05 billion yen ($26 million).

The deal is expected to be inked before the end of this month at the earliest, the report said.

Japan's Chief Cabinet Secretary Osamu Fujimura also told reporters that details of the deal will never be made public.

Despite China's repeated representations, Japan has turned a blind eye to China's demands and deliberately continued the purchase process, which has undermined China's territorial sovereignty, foreign ministry spokesman Hong Lei told reporters at a daily briefing.

"We can't help but ask: where does Japan intend to lead the Diaoyu Islands dispute to?" Hong said.

The latest tension between China and Japan was sparked by the right-wing Tokyo Governor Shintaro Ishihara, who proposed in April the purchase of three of the five uninhabited islands from private owners.

Anti-Japan protests occurred across China in mid-August after Japan detained several Chinese activists who landed on the islands.

"I would like to reiterate that any unilateral move by the Japanese side relating to the Diaoyu Islands is illegal and invalid. The Chinese government's determination to safeguard its sovereignty over the Diaoyu Islands is unswerving," Hong said.

"China is closely following the development of the issue and will take necessary measures to protect its territorial sovereignty," he added.

Kyodo also reported that Japanese Prime Minister Yoshihiko Noda's cabinet would confirm the nationalization of the islands next week and allocate funds for the purchase.

It also said Noda would formally tell Chinese President Hu Jintao about the purchase when the two leaders meet during this weekend's APEC Summit, which will be held in Vladivostok, Russia.

But a later report carried by Kyodo said the "owner" of the Diaoyu Islands was still "hesitating" on the deal with the central government, citing a broker who is pushing the purchase deal between the owner and the Tokyo metropolitan government.

Japan's central government has been trying to justify its purchase by saying it would be much harder to manage if the Tokyo metropolitan government eventually acquired the ownership of the islands.

"The logic is absurd. The restive Japanese right-wing activists led by Ishihara won't stop causing trouble for bilateral ties even if its central government controls the islands," Liu Jiangyong, deputy director of the Institute of International Studies at Tsinghua University, told the Global Times.

"The purchase, no matter who conducts it, is illegal because the Diaoyu Islands belong to China, not a Japanese family," Liu said. "Diplomacy is the only way to solve the dispute. But if Japan stubbornly sticks to military measures to occupy and defend the islands, it should take responsibility for any escalation of tensions."

Zhou Yongsheng, a professor with the China Foreign Affairs University, said, "China should send more civilian fishermen, backed by the Chinese navy, to the waters of the Diaoyu Islands ... We will never fire first but must be well prepared militarily in case of any friction."

"The overall precondition is that the Chinese government has determined to take over control of Diaoyu Islands. It's very hard to make such a decision," Zhou added.

Agencies contributed to this story