A Diet debate halted amid angry scenes when a member heckled a female lawmaker, insinuating a sexual relationship between her and racist anti-Korean activists.

The target was the Liberal Democratic Party's Eriko Yamatani, chief of the National Public Safety Commission and minister in charge of the North Korean abductee issue, as she answered questions on Tuesday about her alleged past links to members of the Zaitokukai far-right group.

"Weren't you intimate with them?" the male heckler called out.

He used the word "nengoro" (intimate), a term often used to insinuate a sexual relationship.

On Wednesday afternoon Kuniyoshi Noda, an Upper House member from the Democratic Party of Japan, owned up to making the offensive comment.

LDP bigwigs Prime Minister Shinzo Abe and Chief Cabinet Secretary Yoshihide Suga slammed the heckler's actions, which took place during a session of the Upper House Budget Committee.

"I deeply regret (that) such an unbearable, humiliating, vulgar jeer should come from the opposition camp," Abe wrote in a Facebook comment on Tuesday.

Yamatani, the victim, was being questioned by Toshio Ogawa about her alleged links to members of Zaitokukai, and an image that showed her posing for a photograph with some of the group's members.