TOKYO/BEIJING - Japan has expressed regret for the intrusion into the Chinese embassy in Tokyo, but this is far from enough, Chinese foreign ministry spokesperson Lin Jian said on Friday, urging Japan to conduct a thorough investigation and give a responsible response.

Japan's Defense Minister Shinjiro Koizumi said Friday it was deeply regrettable that a Self-Defense Forces (SDF) officer, who should be complying with the law and maintaining discipline, had been arrested for breaking into the embassy.

The lawbreaker, a lieutenant in the SDF carrying a knife measuring 31 centimeters in length, chose embassy staff commuting hours to scale the wall to break into the premises and hid in the bushes for a long time, Lin said at a regular news briefing.

"We cannot help but ask, who was he waiting for by setting such an ambush? What did he plan to do? Japan hasn't offered any explanation on these questions yet," Lin said.

On hearing this incident, the Japanese right-wing activists still tried to whitewash the identity of the intruder, claiming that this individual could not be an SDF member, but they were proven wrong, he said.