Japanese Defense Minister Itsunori Onodera (second from right) arrives at a training ground for the Japan Ground Self-Defense Forces' airborne troops as he inspects the New Year exercise in Narashino in Chiba prefecture, suburban Tokyo on Sunday. Photo: AFP

Tokyo has risked further escalating tensions with China over the disputed Diaoyu Islands in the East China Sea by threatening the use of the Japan Self-Defense Forces (SDF) and mulling amending school teaching manuals over the "sovereignty" of the islands.

On Sunday morning, three China Coast Guard vessels carried out patrols in the territorial waters surrounding the Diaoyu Islands, according to the State Oceanic Administration.

In response to the Chinese patrols, Japanese Defense Minister Itsunori Onodera Sunday told reporters, "We can never overlook repeated incursions into territorial waters."

The minister made the remarks after observing the Japanese SDF's elite airborne brigade conducting airdrop drills designed to hone their skills to defend and retake remote islands.

"We need to make diplomatic efforts on one hand. We also want to firmly defend our country's territorial sea and land with the Self-Defence Forces cooperating with the coast guard," he added.

Onodera's mention of the SDF raised concerns over the possibility of military conflicts between Beijing and Tokyo triggered by a clash in the waters near the Diaoyu Islands.

Since Japan's "nationalization" of the islets in September 2012, non-military patrol ships from China and Japan have been shadowing each other in the area.

Liu Jiangyong, a deputy dean of the Institute of Modern International Relations at Tsinghua University, on Sunday told the Global Times that at the current stage it is unlikely that Japan would send the SDF to resolve the dispute, as Japan's pacifist constitution restricts the use of its military.

"However, it is a threatening message by Japan to display its military strength," Liu said.

Meanwhile, Onodera also joined the US in criticizing China's new fishing restrictions in the South China Sea.

The new regulations adopted by China's Hainan Province on implementing the country's fishing law took effect on January 1.

The amended regulations require foreigners and foreign fishing vessels to obtain approval from the central government of China before entering waters under its jurisdiction.

"I'm afraid not only Japan but international society as a whole has a concern that China is unilaterally threatening the existing international order" with its new restrictions in the South China Sea and the creation of an Air Defense Identification Zone in the East China Sea, said Onodera.

According to Liu, the Japanese defense minister's comment on China's new fishing law was a move to rally support among Southeast Asian countries to contain Beijing, as several countries in the region are locked in territorial disputes with China in the South China Sea.

Separately, Japan's education ministry is planning to describe the Diaoyu Islands and a group of islands in the center of a territorial dispute between Tokyo and Seoul as inherent parts of Japan's territory in new guidelines for middle and high schools, reported Japanese broadcaster NHK.

According to the report, the change will be made in a supplement to the government's new guidelines for textbook publishers and teachers. The existing supplement does not contain descriptions about the Diaoyu Islands, and neither do some textbooks.

The ministry expects the guidelines will be reflected in textbooks to be published for the 2016 school year and after, according to NHK.

"It will intensify the disputes between China, South Korea and Japan. At the same time, Japanese students will be misled by the textbook if they are not clear about the facts and this affects their sentiment toward their neighbors," Liu said.

Agencies contributed to this story