TOKYO - The Japan Restoration Party's co-head Shintaro Ishihara slammed the party's another leader, Toru Hashimoto, over the latter's controversial wartime sexual slavery remarks that have hurt public support for the party, according to local media.

Ishihara said the improper words made by Hashimoto over the wartime military brothels a "great nuisance", adding that Hashimoto should take the responsibility if their party falls short of expectations in the upper house election, Japan's Kyodo News reported late Tuesday.

The report said the criticism by the former Tokyo governor would deepen the conflicts within the party, which is a major opposition after the largest Democratic Party of Japan.

Hashimoto said on May 13 that the "comfort women" system is "necessary" to keep disciplines in Japanese army in wartime and suggested the US servicemen to "use legal adult entertainment".

Ishihara's criticism, ahead of the upper house election, is apparently in a move to retake public support for the party as Hashimoto's remarks drew wide condemnations within and outside Japan.