Japan has asked China on three occasions to urge authorities to take steps to ensure the safety of Japanese soccer team members and fans at the ongoing Asian Cup soccer tournament, Masatoshi Abe, senior vice foreign minister, said Wednesday.

The complaints were made in response to heightened concerns over the tumultuous booing targeted at the Japanese during the games that apparently reflects anti-Japanese sentiment fueled by Japan's wartime aggression in China.

The booing "is deeply regrettable," Abe told a regular news conference. "Since (the tournament) is being held to promote friendship and goodwill, (the Chinese fans) should act in a sportsmanlike manner."

Japan's first complaint was lodged July 26 to municipal officials in the city of Chongqing, which was followed by a second protest July 28 via the Japanese Embassy in Beijing, according to the Foreign Ministry. The most recent action was taken Tuesday via the Chinese Embassy in Tokyo, an official said.

Abe said the government might lodge a similar request before the tournament's finals between Japan and China on Saturday in Beijing.

At the same time, however, he noted that Chinese authorities have upgraded their security measures for Japanese players and fans, saying there were "improvements" on the security front during Tuesday night's semifinal match between Japan and Bahrain in Jinan, China.

The Chinese increased the number of security personnel in and around the stadium, made Japanese interpreters available and checked at the gates to see whether Chinese fans had banners with anti-Japanese slogans on them, Abe said.

The actions of Chinese fans, which included throwing objects at Japanese spectators, have prompted some Liberal Democratic Party lawmakers to demand that the Japanese government strongly protest.