Japan on Wednesday lodged a protest with China over the launch of English and Japanese versions of a Chinese government website asserting Beijing’s claim to the Japanese-administered Senkaku Islands in the East China Sea.

Chief Cabinet Secretary Yoshihide Suga said the website, the Chinese version of which was set up in December, “distorts facts and reiterates China’s own claim,” which Tokyo “can never accept.”

“Historically and diplomatically, the Senkaku Islands are our country’s inherent territory, and in reality, we have valid control over them,” the top government spokesman said at a news conference.

Suga said that when China launched the site in December, Japan filed a protest with China and demanded that it be removed immediately.

Quoting a statement by China’s State Oceanic Administration, the official Xinhua News Agency reported Wednesday the website “will help the international community to know the truth and further demonstrate China’s indisputable sovereignty over Diaoyu Dao.”

The website, titled The Inherent Territory of China, lays out the country’s claims on the islands, which it calls Diaoyu, with a series of documents, including legal texts and historical maps from as early as the 16th century.

The site, which is published by the State Oceanic Administration, claim that the islands came into Japan’s possession illegally as part of a post-World War II “backroom deal” with the United States.

In addition to promoting China’s position on the islands’ ownership, the site also includes a news section, which details visits by the country’s coast guard into waters surrounding the uninhabited islets in the East China Sea.

So far in 2015, according to the English-language site, 10 vessels have carried out patrols in the area on six separate occasions, with the most recent taking place last week.

During the same period last year, China carried out four patrols, with eight vessels, it said.

The activities have been an irritant to Japan, which has administrative control over the islands.

Although China has long insisted it is the territory’s rightful owner, the dispute escalated dramatically in 2012, following the Japanese government’s purchase of several of the islets from a private owner.

In the aftermath, Chinese and Japanese ships and aircraft engaged in a series of close encounters near the islands, including one incident in which a Chinese jet reportedly came within 30 meters of a Japanese surveillance plane.

In recent months the two governments have restarted a series of talks to establish maritime crisis prevention mechanisms intended to lower the possibility of a dangerous encounter between their forces in the area.

Taiwan also lays claim to the islands, which it calls Tiaoyutai.