Three banks led by Royal Bank of Scotland threatened to launch a hostile bid for ABN AMRO in a sign of their growing resolve to elbow aside rival Barclays to secure the world's biggest banking takeover.

In response, ABN lifted a contentious "standstill" condition attached to opening its books to the group, saying that it was "committed to exploring the consortium's proposal in a constructive manner".

The RBS consortium, which earlier this week proposed a €72 billion ($98 billion) bid for ABN, had opposed the clause. Their proposed offer could trump an agreed all-share deal from Britain's Barclays worth around €65 billion at current prices.

The consortium, which also includes Santander and Fortis, formally notified ABN earlier yesterday of their intention to make a public offer.

"Under Dutch regulation, this is effectively the announcement of a hostile bid," analyst Jean-Pierre Lambert at Keefe, Bruyette & Woods said. "This indicates the consortium is quite serious."

By lifting the provision and offering the consortium due diligence access to its books, ABN may enter buyout talks with the consortium, a step which ABN shareholders demanded in an annual meeting held on Thursday.

The shareholders also backed a motion to break up or sell the bank.

The RBS-led group has not ruled out sweetening its offer and has leeway to do so, sources familiar with the matter said.

The banks, which say that they want to meet ABN's board as soon as possible, have also said their proposed offer is conditional on ABN scrapping the planned $21 billion sale of US unit LaSalle - a key asset for suitor RBS - to Bank of America.

The LaSalle sale, which includes a "go-shop" clause allowing ABN until midnight on May 6th to seek higher bids, also prompted the consortium's statement yesterday. - (Financial Times Service)