YOKOTA AIR BASE, Japan — The killing of a Japanese mob boss in Tokyo on Monday, and the resulting retaliatory violence between Japan’s top two rival crime syndicates, has led the Japanese National Police Agency and U.S. Forces Japan to issue a warning to Americans in the Tokyo and Fussa areas.

Officials are advising Americans to consider avoiding the Roppongi area of Tokyo for the next several days, in case there is any more retaliation.

In addition, residents of Yokota Air Base and the surrounding area are also advised to avoid the Bar Row area of Fussa, a region also controlled by the Tokyo- based Sumiyoshi-kai crime syndicate.

Ryoichi Sugiura, 43, a senior member of the Sumiyoshi-kai syndicate, was shot and killed in his car on Monday morning in the Nishi-Azabu area of Tokyo, according to Associated Press reports. The killing has since sparked a series of retaliatory shootings aimed at the offices of Japan’s largest gang, the Yamaguchi-gumi.

The Yamaguchi-gumi syndicate originated in Kobe, Japan, but in recent years has begun expanding in influence in downtown Tokyo, according to the Associated Press.

While Americans are not believed to be the target of violence, USFJ officials say that informing Americans about the shootings will help prevent anyone from being in the wrong place at the wrong time.

No official restrictions to Tokyo have been issued, said Capt. Jason Medina, a USFJ spokesman.

“We’re just telling people to be extra vigilant when they go out,” he said.

At Yokota, base leadership is spreading the word through command channels and by e-mail, advising airmen to stay out of Bar Row and Roppongi, said Capt. Warren Comer, a spokesman for the 374th Airlift Wing.

An estimated 87,000 gang members are in Japan, according to 2005 National Police Agency estimates.

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