TOKYO -- Left-wing radicals are reportedly suspected after an "improvised launch device" was used near a U.S. air base in Japan late Thursday.
Tokyo Metropolitan Police received several reports of an explosion near Yokota Air Force Base around 11:30 p.m. local time (9:30 a.m. ET). Authorities later confirmed that a "projectile" had been fired.
Police said "two pipes, a lead wire and dry batteries" were later recovered from a field about 300 yards from the military site.
A U.S. military spokesman told Reuters that no injuries were reported and "no damage or impact points" had been located at the base.
National broadcaster NHK reported that left-wing activists were suspected to be behind the attack. NBC News was unable to independently confirm the report.
Similar incidents targeted Yokota air base in Oct. 2009 and July 2007. No injuries were reported during either attack.
Reuters contributed to this report. Jason Cumming reported from London.