TOKYO, Japan -- The suspected killer of Japan's former prime minister Shinzo Abe admitted targeting the politician and said he held a grudge against an organisation he believed Abe was connected to, police said Friday.

Senior police officers in the western region of Nara, where the murder took place, named the suspect as unemployed 41-year-old Tetsuya Yamagami, who said he had used a handmade gun.

"That's the suspect's assertion, and we have determined that (the gun) is clearly handmade in appearance, although our analysis is currently ongoing," an officer told reporters.

Police declined to give details of the "particular organisation" mentioned by the suspect, saying investigations were ongoing, but several Japanese media outlets described it as a religious group.

Yamagami was pictured at the scene holding a large boxy black object that appeared to have two barrels.

Officers in protective gear began searching the suspect's home after 5pm and have confiscated "several handmade gun-like items".

The suspect, who addressed police in a "matter-of-fact way", told officers he had worked for the Maritime Self-Defense Force -- Japan's navy -- for three years from 2002, but these details are also under investigation.

Yamagami also told police he had learned about Abe's visit online, the officers said.

They added that they were probing whether there were any problems with security at the campaign event where the assassination took place on Friday morning.

"We will take appropriate measures if problems were discovered."