The man accused of assassinating former Japanese prime minister Shinzo Abe has apologised to the ex-leader's family for the first time.

Tetsuya Yamagami, who earlier pleaded guilty to murder, told the court on Thursday that he felt "deeply sorry" towards Abe's widow, Akie.

Yamagami used a homemade gun to shoot Abe during a political campaign event in the western city of Nara on 8 July 2022. He died in the hospital on the same day.

Abe's death sent shockwaves around the world. He was known for his hawkish foreign policy and a signature economic strategy that popularly came to be known as "Abenomics".

"I have caused [the family] three and a half years of suffering... I have no excuse," Yamagami told the court on Thursday, according to local media.

He reportedly told investigators he attacked Abe because he blamed the ex-prime minister for allegedly promoting the Unification Church, which Yamagami said had bankrupted his mother and the wider family.

Yamagami's allegations prompted investigations into the Unification Church, which started in South Korea and is known for its mass weddings.

In March this year, a Tokyo court ordered the church to disband - a ruling that the church said it would "fight to the end".

The Unification Church has drawn controversy even before Abe's assassination, for teaching that marriage is central to spiritual salvation.

Abe's grandfather Nobusuke Kishi, who was also Japan's prime minister, was known to have been close to the Unification Church because of its anti-communist nature. Abe himself had spoken at events related to the group.

During a hearing last month, prosecutors read out a statement from Abe's widow in which she wrote: "The sorrow of losing a husband will not be relieved."