Shinsei Bank said Thursday major online financial firm SBI Holdings Inc. has failed to give a sufficient explanation on events leading up to its abrupt launch of an unsolicited takeover bid for the bank.

Shinsei Bank has yet to clarify its stance on the planned takeover but pointed out in a statement addressed to shareholders that some information given by SBI is "inaccurate" or "insufficient."

With its ambitious goal to become the fourth megabank in Japan, SBI is seeking to make Shinsei Bank a subsidiary by raising its stake to a maximum of 48% from the current 20% in a tender offer announced last week worth around ¥116.4 billion ($1.06 billion).