Two small, homemade bombs went off early June 17 at the Kawasaki home of a senior Transport Ministry official, destroying a portion of the wall surrounding the house, police said. No one was injured in the explosion.

Police suspect ultra-leftists are responsible for planting the crude, timed devices at the home of Masanobu Koyama, 52, councilor of the Transport Ministry's Secretariat, they said. No group has claimed responsibility for the blast.

Investigators discovered pieces of lead and flashlight batteries in the 40-cm space between the concrete wall and the house in Nakahara Ward. They believe two timed, plastic pipes stuffed with gun powder were planted at the base of the wall. The blast destroyed a 2-meter area of the concrete wall as well as the house's kitchen window, police said.

Koyama is in charge of Diet affairs and public relations. Leftist guerrillas have targeted the official after it was unveiled earlier this month that Japan-U.S. defense guidelines include the use of civilian airports in the event of an emergency. The ministry has also been a target of far-left groups because of its leading role in the construction of Narita airport.