Tokyo ? Japanese police were investigating a suspected extremist attack on the U.S. Army after two small explosions occurred outside a military base south of Tokyo, police said today.

There were no reports of injury or damage at Camp Zama or from nearby residents, Kanagawa prefectural police spokesman Hiroyoshi Ichikawa said.

Investigators found a pair of metal tubes planted in the ground at a nearby park. They were believed to be used as rocket launchers and pointed toward the base, Ichikawa said.

He said investigators suspected an attack by leftist extremists, but could not rule out a possibility of a terrorist attack.

The Army was investigating the blast, said an official at Camp Zama who spoke on condition of anonymity, adding that there were no reports of injuries or damage.