ABN Amro's board has announced it is dropping its support for Barclays Bank's buyout bid.
However, the firm added that it will not be endorsing the Royal Bank of Scotland-led consortium's higher offer, which also includes a larger cash component.
A statement issued by ABN Amro, which was previously perceived to favour Barclays' bid, said that it could not recommend either offer owing to "significant unresolved questions".
The statement added: "ABN Amro will further engage with both parties with the aim of continuing to ensure a level playing field and minimising any of the uncertainties currently associated with the offers with a view to optimising the attractive alternatives available to ABN Amro's shareholders."
Barclays' bid currently stands at $87.5 billion, while the consortium's rival offer is worth $96.6 billion.
News of developments in the takeover battle follows reports that a group of hedge funds approached Barclays about acquiring voting-rights shares in consortium partner Fortis.
Had Barclays accepted the plan, the hedge funds would have used the shares to vote against Fortis' proposed £8.7 billion rights issue, which is intended to raise funding for the ABN Amro takeover.