TOKYO - Two improvised rocket launchers were fired near a US military base near Tokyo, police said Friday, although no-one was hurt and no damage was done.
"The incident occurred at 11:30 pm on Thursday. Flying objects were launched near the US military's Yokota airbase," a spokesman for Tokyo Metropolitan Police said.
"Several reports were made by neighbours that they had heard explosions at about 11:30 pm. Police discovered two steel pipes, two wires, batteries, and so forth.
"No damage has been reported so far and police have not found the projectiles."
Local media reported the pipes were buried in the ground, with the upper end pointing in the direction of Yokota Air Base.
There have been no claims of responsibility, but police believe it may have been a guerrilla attack by extreme leftists, Jiji Press and other media said.
Broadcaster NTV reported police were concentrating their investigations on a hard leftist group because the incident came just hours after they arrested a top-ranking member on Thursday.
A similar incident occurred four years ago, when police raided hideouts of the same leftists, NTV said.
Japan is host to almost 50,000 US service personnel and their families. The two countries have a mutual defence agreement that, in practice, means Tokyo is given shelter under Washington's significant security umbrella.
But many people in Okinawa, where the bulk of US troops are based, resent their presence and an increasingly vocal campaign wants them to leave. However, reports of violence to this end are not common.
The incident also comes as tensions run high in the region between China and Japan with the focus on a group of disputed islands in the East China Sea.