China has lodged strong demarches with Japan over a break-in at its embassy in Tokyo, urging the Japanese government to conduct a thorough investigation into the extremely grave incident.

Speaking at a regular news briefing in Beijing, Foreign Ministry spokesman Lin Jian said an individual claiming to be an active-duty officer of Japan's Self-Defense Forces scaled the boundary wall and forcibly entered the Chinese embassy in Tokyo on Tuesday morning.

While admitting his actions were illegal, the individual threatened to kill Chinese diplomatic personnel in the so-called "name of god", Lin said, adding that China is deeply shocked by the incident, which was "extremely egregious in both nature and impact".

The spokesman noted that the break-in seriously violated the Vienna Convention on Diplomatic Relations, and emphasized that such incidents pose a grave threat to the safety and security of Chinese diplomatic personnel and facilities in Japan.

The incident once again highlights the dangers of the rampant spread of far-right thinking and neo-militarism in Japan, Lin said, adding that it also exposes the toxicity of the Japanese government's erroneous policies on vital issues concerning China-Japan relations, including history and the Taiwan question.

He said that Japan has failed to properly supervise and discipline the SDF, and has not fulfilled its responsibility to protect Chinese diplomatic and consular premises and personnel.

"China demands that Japan immediately carry out a thorough investigation, severely punish those responsible for the break-in, and give China a responsible account of the incident," Lin said.

Japan must effectively guarantee the safety and security of Chinese diplomatic and consular premises and personnel, reflect on and correct its erroneous policies on China, and fundamentally prevent such incidents from happening again, he said.

"The international community should remain highly vigilant against the dangerous trend of Japan's accelerating rightward shift and its loss of control over the expansion of the SDF," he added.

At the same news briefing, Lin also responded to Japan's revised description of bilateral relations in its annual diplomatic report, saying that the current difficulties in Sino-Japanese ties stem from Japanese Prime Minister Sanae Takaichi's erroneous remarks related to Taiwan.

"If the Japanese side is truly sincere about improving and developing bilateral relations, it should abide by the four political documents between China and Japan and its own commitments," he said, urging Japan to retract the remarks on Taiwan and take concrete actions to safeguard the political foundation of the two nations' ties.

mojingxi@chinadaily.com.cn