Tokyo prosecutors on Saturday questioned former state justice minister Kakizawa Mito on a voluntary basis on suspicion of vote-buying for a mayoral candidate in Tokyo's Koto Ward in April.

Prosecutors say the 52-year-old Lower House member is suspected of violating the public offices election law.

Kakizawa's office backed former Koto Ward Mayor Kimura Yayoi in the April mayoral election instead of a candidate supported by the governing Liberal Democratic Party, to which Kakizawa belonged at the time.

Kakizawa's office is alleged to have provided cash to some ward assembly members before and after the election.

The office is also suspected of having given a former assembly member who backed Kimura 200,000 yen, or about 1,400 dollars, every month after the election as an advisory fee.

Informed sources say Kakizawa explained to prosecutors that he had no intention of buying votes.

The sources add that Kakizawa denied involvement in his office allegedly providing remuneration to more than 10 campaign staff of the former mayor.

Kakizawa's office is suspected of having advised Kimura's campaign in the use of paid online ads.

The sources say Kakizawa said he was not aware of the illegality of such advertisements.

Prosecutors searched Kakizawa's office, as well as the homes of his secretaries and others in November, and raided his office in the Diet members' building in Tokyo and his home this month.