Japan's police chief has said he will resign over the killing of former prime minister Shinzo Abe.

Itaru Nakamura, head of the national police agency, said he wanted to take responsibility for the July 8 shooting.

An investigation has found there were serious flaws in how the ex-PM was protected.

Mr Abe was shot while speaking at a political campaign event in the city of Nara.

The 41-year-old gunman was able to walk up behind Mr Abe and shoot him with a homemade gun as he was giving a speech.

The 67-year-old suffered two bullet wounds to his neck and damage to his heart, doctors said.

Local police have already acknowledged "undeniable" flaws in security for Mr Abe.

"In the process of verifying our new security plan, we have come to realise that our security duties would need a fresh start," Mr Nakamura told a news conference as he announced his resignation.

Mr Abe was Japan's best-known politician and longest-serving prime minister, but security was comparatively light as he delivered a stump speech on a street in the western region.

Security experts who have reviewed footage of the attack have previously told news agency Reuters that bodyguards could have saved Mr Abe by shielding him or pulled him from the line of fire in the 2.5 seconds between a missed first shot and the second, fatal round of gunfire.

The suspect, Tetsuya Yamagami, was arrested at the scene and admitted to shooting Mr Abe, police have said.

He confessed that he targeted Mr Abe due to his belief that he was linked to a religious group - which Yamagami said had financially ruined his mother.