Sources say prosecutors in Tokyo have asked a former state justice minister to turn himself in for questioning over alleged vote-buying in a local mayoral election.

The prosecutors are expected to question 52-year-old lawmaker Kakizawa Mito as early as Thursday on suspicion of violating an election law.

In the April mayoral election of Tokyo's Koto Ward, Kakizawa backed Kimura Yayoi instead of a candidate supported by his own Liberal Democratic Party.

It has been revealed that Kakizawa's office gave cash to Koto Ward assembly members as instructed by the lawmaker, and remuneration to Kimura's election campaign staff.

Sources say Kakizawa told prosecutors in voluntary questioning that the payments to the assembly members were his mid-campaign contributions for an assembly election held at the same time as the mayoral one. He added that he had no intention of buying votes.

He also denied involvement in the payments to the election campaign staff.

Kakizawa resigned as state justice minister in October to take responsibility for recommending that Kimura's camp use paid online ads for her election campaign.

He also left the LDP on December 14th, when his offices were raided by prosecutors.