A 2013 assault on a nurse by a crime syndicate in Fukuoka Prefecture was ordered by its 70-year-old boss who was dissatisfied with the results of plastic surgery on his genitals, prosecutors said.

Satoru Nomura, head of the Kudo-kai syndicate, launched a campaign of "organized retaliation" as he "unjustifiably resented the failed surgery," the prosecutors said in their opening statement Monday for the Fukuoka District Court trial of a former senior member of the group who was allegedly involved in the case.

The female nurse, who was part of the surgical team when Nomura underwent the operation at a cosmetic surgery clinic in August 2012, was stabbed in the assault.

The former senior member, Yoshinobu Nakata, denied conspiring with the gang's leaders to attack the nurse.

Nakata, 41, admitted that he had given a lift to a perpetrator in the assault but said he had no intention of killing her. He also said he did not know whether the assault was organized by the Kudo-kai.

According to the prosecutors, Nakata, who has also been indicted over two other attacks, allegedly stabbed the nurse in the neck and chest in January 2013 on a street in the city of Fukuoka.

Nomura and other senior Kudo-kai members have been charged in relation to all three attacks and the focus is on whether the prosecutors can prove they were ordered by Nomura.

During Monday's trial session, the prosecutors used phone conversation records resulting from approved wiretaps to argue that Kudo-kai members had communicated with each other on mobile phones to plan the attack.