The man from Guangzhou, who came to South Korea on a tourist visa on Dec. 26 via Japan, claimed he also set fire to Tokyo's Yasukuni Shrine before leaving that country, Park said.

Before entering South Korea, Liu had stayed in Japan for two months since October as a volunteer to help victims of March's massive earthquake and tsunami, the officer added.

"We discovered Liu is the one who claimed to have set fire to the door of Japan's Yasukuni Shrine last month," Park said.

The controversial shrine, often seen as a symbol of Japan's wartime aggression, is regularly a source of friction with Japan's neighbors who say it honors those responsible for war crimes.

According to officials, Liu said he attacked the embassy to protest Japan's refusal to apologize for its war crimes, claiming his deceased grandmother on his mother's side was a former Korean sex slave.

Although no injury or property damage was reported in the incident, investigators are considering requesting a warrant to arrest the Chinese national considering the seriousness of his alleged crime.

Historians say tens of thousands, perhaps hundreds of thousands, of women from Korea and other Asian countries were forced to serve as sexual slaves for front-line Japanese soldiers during the war.

The subject of sex slaves, euphemistically called "comfort women," is one of the most emotional unresolved issues between South Korea and Japan. (Yonhap News)