It is far from enough for Japan just to express regret on the incident of a Self-Defense Forces officer illegally breaking into the Chinese embassy in Japan, the Chinese Foreign Ministry said on Friday.

Lin Jian, spokesman for the ministry, again urged Tokyo to conduct a thorough investigation and give Beijing a responsible response.

Japan's Defense Minister Shinjiro Koizumi said on Friday it was deeply regrettable that an SDF officer, who should be complying with the law and maintaining discipline, had been arrested for breaking into the Chinese embassy in Japan.

On Tuesday, an individual who identified himself as an active-duty officer in Japan's SDF, alleged to be second lieutenant Kodai Murata, 23, stationed at Camp Ebino in Miyazaki Prefecture, scaled a wall and broke into the Chinese embassy in Tokyo. Admitting that his actions were illegal, the individual threatened to kill Chinese diplomats in the "name of God".

Murata was arrested by police and transferred to prosecutors on suspicion of illegal entry on Thursday, according to local media.

Noting that the individual illegally broke into the embassy with a 31-centimeter-long knife during commuting time, and hid in the bushes for a long time, Lin asked: "Who was he waiting for by setting such an ambush? What did he plan to do?"

Japan has yet to answer these questions, Lin said, adding that Japanese right-wing activists even tried to whitewash the illegal action after hearing about the incident.

They believed that the individual must not be a member of the SDF, but the facts speak louder than their words, Lin added.

Voices within Japan, including those expressed on social media and other online platforms, have criticized the act as serious and questioned the Japanese government's handling of the situation.

Influence of far-right

Kazunaga Kitanaka, secretary-general of the Tokyo Federation of the Japan-China Friendship Association, said he was shocked and outraged by the incident in which an active-duty officer of Japan's SDF illegally broke into the Chinese embassy in Japan.

Noting that the individual was a second lieutenant rather than an ordinary soldier, he said the act was clearly influenced by far-right ideology and inappropriate rhetoric, and called on the Japanese government to respond promptly and hold those responsible accountable.

He stressed the need for a thorough investigation into the background of the case and warned against hastily attributing it to personal motives.

Hiroshi Shiratori, a professor at Hosei University in Tokyo, said the incident is absolutely unacceptable under international law and warned that if Japan treats the matter merely as "regrettable", it may find it difficult to demand sufficient apologies in the future when Japanese diplomatic personnel face similar incidents overseas.

Masahiro Yamazaki, a Japanese historian, described the incident as serious and questioned whether Prime Minister Sanae Takaichi, as the commander-in-chief of the SDF, should explain it. He said the Japanese government's handling of the case could significantly affect the future direction of Japan-China relations and must be addressed with seriousness.

The Chinese embassy in Japan has lodged solemn representations and a strong protest with the Japanese side, demanding that Japan conduct a thorough investigation, hold those responsible accountable, and provide a responsible explanation.

Contact the writers at houjunjie@chinadaily.com.cn