Feb. 12 (Bloomberg) -- A small explosion went off near a U.S. military base outside Tokyo, a Pentagon spokesman said.

``To my knowledge, there are not reports of any injuries,'' the spokesman, Air Force Major David Smith, said in a telephone interview.

Smith had no more immediate information about the blast, which took place at Camp Zama, a U.S. Army garrison 25 miles southwest of Tokyo.

A Japanese news report said local police suspect a bomb and that it was part of an attempted guerilla attack on the base, the Associated Press reported. Kyodo News agency reported that the police found a ``launch pad'' near the base, AP said.

Japanese police in 2002 found a metal projectile and a crude mortar after two blasts were heard then outside Camp Zama, AP said. The news service added that leftists in Japan have used projectile launchers in symbolic attacks against U.S. military bases or sites with ties to the Japanese royal family.

To contact the reporter on this story: Judy Mathewson in Washington at jmathewson@bloomberg.net

Last Updated: February 12, 2007 12:21 EST