TOKYO (Reuters) - Bain Capital plans to launch a tender offer for Fuji Soft shares even without the approval of the target firm's board of directors, the U.S. private equity firm said on Wednesday.

The announcement came a day after the Japanese IT firm reaffirmed its support for the second stage of a tender offer buyout from rival KKR, turning down a higher offer from Bain.

Bain has said it would begin its tender offer only with the approval of Fuji Soft's board. But it now plans to "promptly launch our tender offer if (KKR's) second round of the tender offer ends unsuccessful or will be withdrawn," Bain said in its presentation file.

Bain also said it has "strong concerns and distrust" in Fuji Soft's response to its proposal.