The small opposition Your Party decided Tuesday to cancel planned electoral cooperation with the Japan Restoration Party, following controversial remarks by its co-head and Osaka Mayor Toru Hashimoto concerning wartime sexual servitude.
"Given differences in values, we have to totally review the relationship," Your Party leader Yoshimi Watanabe told a meeting of party executives.
The two opposition parties had been discussing a possible alliance in the Tokyo metropolitan assembly election next month and the House of Councillors poll expected in July.
For the upper house election, they had agreed to back the same candidates in some constituencies to unite forces against Prime Minister Shinzo Abe's Liberal Democratic Party.
"This is a tough environment. But we will fight head-on," Osaka Gov. Ichiro Matsui, who doubles as Japan Restoration's secretary general, told reporters on Tuesday.
Hashimoto stirred controversy recently with remarks seen as justifying the practice of sex slavery for the Japanese military in Asia during World War II.