Japanese investigators have found a dent on the wall of a warehouse 40 meters away from the location where an explosive was thrown at Prime Minister Kishida Fumio.

Officials are analyzing the structure and the strength of explosives confiscated from the site to determine how the incident took place.

The prime minister was about to give a speech at a fishing port in the western city of Wakayama on Saturday when the explosion occurred. He was there to support a Lower House by-election candidate.

Two people, including a police officer, were injured.

A bomb squad confiscated one of the two cylindrical devices that had reportedly been in the possession of 24-year-old suspect Kimura Ryuji, who was arrested on the spot.

Police located the explosive Kimura had thrown on fish tank netting next to a warehouse about 40 meters from the blast site.

Police say the dent on the warehouse wall, which resembled the cross-section of a cylinder, was apparently made when the explosive struck it.

On Monday, investigators began analyzing the structure and the strength of the explosive devices.

Police have also seized tools and what appear to be gunpowder and metal pipes from the suspect's home in the city of Kawanishi, Hyogo Prefecture. Officials believe the bomb was handmade, but the suspect is reportedly remaining silent.