TOKYO — Japanese police on Wednesday raided 15 operational bases of an anti-U.S. military, left-wing extremist group.

No arrests were made of any Kakurokyo members during the raids, which took place in eight prefectures, a Tokyo Metropolitan Police spokesman said Thursday. Kakurokyo is believed to be responsible for homemade mortar rockets found in November 2009 just outside Yokota Air Base and December 2009 near Naval Air Facility Atsugi.

Tokyo police refused to disclose whether any items were confiscated during Wednesday’s raids. Police confiscated more than 130 items – including computers and propaganda – during similar raids on the group in August, Kanagawa Prefecture police said at the time.

The raids occurred less than three weeks before the start of the Asia-Pacific Economic Cooperation Summit in Yokohama, which will include world leaders and senior officials from the United States and at least 20 other nations.

Although Tokyo police would not comment on a possible connection, other Japanese police departments have attributed raids on suspected criminal groups to precautionary measures in advance of the summit.

Police also raided Kakurokyo locations last year on suspicion that the group had fired projectiles at Yokosuka Naval Base in September 2008, when a mortar blasted a hole through the balcony of an off-base home. They confiscated about 60 items at that time, but also made no arrests, police said.

The group later claimed responsibility in a letter sent to various newspapers stating the attack was the first of an effort to stop the Navy from forward deploying the aircraft carrier USS George Washington to Japan.

The Mainichi Shimbun also reported Wednesday that police connected Kakurokyo to each incident after comparing the mortars.

Kakurokyo, also known as the Revolutionary Workers’ Council, is one of about 50 so-called New Left groups operating in Japan, according to the U.S. Department of Homeland Security’s National Consortium for the Study of Terrorism and Responses to Terrorism, based at the University of Maryland.

The majority of such groups were formed after the 1955 decision of the Japanese Communist party to abandon violent tactics. Some members, however, chose to start new groups that remained committed to terrorist acts, according to the consortium’s website.

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Hana Kusumoto is a reporter/translator who has been covering local authorities in Japan since 2002. She was born in Nagoya, Japan, and lived in Australia and Illinois growing up. She holds a journalism degree from Boston University and previously worked for the Christian Science Monitor’s Tokyo bureau.

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