Japan's Sumitomo Mitsui Financial Group has unveiled plans to merge with ailing rival UFJ, potentially derailing an existing bid from Mitsubishi Tokyo.
UFJ and Mitsubishi had hoped to seal a deal by the autumn
The move casts doubt on the UFJ-Mitsubishi merger, a deal which would create the world's biggest bank.
Sumitomo's president, Yoshifumi Nishikawa, said the bank aimed to table a merger proposal later on Friday.
UFJ said it would continue to pursue a tie-up with Mitsubishi, but would weigh up Sumitomo's proposal.
"We are willing to listen to what Sumitomo Mitsui has to say," a UFJ spokesman said.
A rival offer from Sumitomo has been on the cards since Tuesday, when the bank won a court order blocking merger discussions between UFJ and Mitsubishi.
Sumitomo argued that the proposed tie-up would breach an existing agreement it had with UFJ to buy its trust banking operations.
Mitsubishi and UFJ had originally hoped that their merger, which would create a combined group with 188.7 trillion yen ($1.7 trillion ; £0.9 trillion), would be complete by the autumn.
Osaka-based UFJ, the smallest of Japan's 'Big Four' banks, is keen to join forces with a larger rival.
Weighed down by bad loans, the bank crashed to loss of 402 billion yen in its most recent financial year, prompting the resignation of senior executives.