Pfizer said on Monday it had abandoned its current attempt to buy AstraZeneca for nearly 70 billion pounds ($118 billion) as a deadline approached without a last-minute change of heart by the British drugmaker.

Under U.K. takeover rules, Pfizer had until 5 p.m. (12 p.m. Eastern time) on May 26 to make a firm offer or walk away. Its decision to quit its bid, at least for now, was widely expected after AstraZeneca refused Pfizer's final offer of 55 pounds a share.

"Following the AstraZeneca board's rejection of the proposal, Pfizer announces that it does not intend to make an offer for AstraZeneca," Pfizer said in a short news release.

The biggest U.S. drugmaker promised it would not go hostile, leaving the fate of what would have been the world's largest drug merger in the hands of its target, whose board would have had to make a U-turn to get a deal done.

"We continue to believe that our final proposal was compelling and represented full value for AstraZeneca based on the information that was available to us," said Ian Read, Pfizer's chairman and chief executive.

AstraZeneca chairman Leif Johansson said in a statement Monday, "We note Pfizer's confirmation that it no longer intends to make an offer for AstraZeneca. We welcome the opportunity to continue building on the momentum we have already demonstrated as an independent company."

British rules require a cooling-off period at this stage. AstraZeneca could reach out to Pfizer after three months, and Pfizer could take another run at its smaller British rival in six months whether it is invited back or not.

Pfizer's final offer was at a price point that many analysts and investors previously suggested would bring AstraZeneca to the table for serious negotiations.

But in rejecting an earlier offer of 53.50 pounds as undervaluing the company, the British group indicated it needed a bid more than 10 percent higher, or at least 58.85 pounds per share, for its board to consider a recommendation.

Pfizer had urged AstraZeneca shareholders to agitate for engagement, and several expressed disappointment at its intransigence, although others — encouraged by AstraZeneca's promising drug pipeline — backed the firm's stand-alone strategy.

What happens next will depend upon whether AstraZeneca's share price deteriorates in the coming weeks and how hard its shareholders push for it to revisit a deal with Pfizer.

BlackRock, AstraZeneca's biggest shareholder, backed the board's rejection of Pfizer's offer of 55 pounds a share but urged it to talk again in the future.