Tokyo (AFP) - Women in Tokyo are threatening a sex boycott against any man who votes for the front-runner in this weekend's gubernatorial election, in protest at his claim that menstruation makes women unfit for government.

A Twitter campaign group based in the capital which bills itself as "The association of women who will not have sex with men who vote for (Yoichi) Masuzoe," has garnered almost 3,000 followers since it launched last week.

Although the founders have not identified themselves, in their profile they said: "We have stood up to prevent Mr. Masuzoe, who makes such insulting remarks against women...We won't have sex with men who will vote for Mr. Masuzoe."

Masuzoe, 65, a former political scientist who became a celebrity through TV talk shows before getting involved in politics in 2001, is widely seen as an establishment figure in a country where gender roles remain very distinct.

In 1989, he told a men's magazine that it would not be proper to have women at the highest level of government because their menstrual cycle makes them irrational.

"Women are not normal when they are having a period... You can't possibly let them make critical decisions about the country (during their period) such as whether or not to go to war," he said.