Endurance Specialty Holdings Ltd., the Bermuda-based provider of property and casualty insurance, announced a $3.2 billion offer to buy Aspen Insurance Holdings Ltd. after the target company turned down its proposal.

Endurance offered to pay $47.50 per share, compared with the April 11 closing price of $39.37, Endurance said today in a statement. Both companies are based in Bermuda.

“Despite our repeated attempts since late January to engage in confidential and friendly discussions, Aspen’s board and management have rebuffed our proposal,” Endurance said in the statement. The refusal to hold discussions denies Aspen’s shareholders “the ability to understand and attain the clear financial, operational and strategic benefits of this transaction,” Endurance said.

Mid-sized insurers have been combining or joining with larger companies to diversify risk and gain scale to take on bigger accounts from primary carriers. Endurance said its offerings in crop insurance would complement Aspen’s products, including its operations in the Lloyd’s of London market.

Endurance said its return on equity and earnings per share would gain in 2015 under a takeover through about $100 million in annual “synergies,” including cost cuts, underwriting improvements and better chances for capital management.

Steve Colton, a spokesman for Aspen, didn’t immediately respond to a phone call and e-mail requesting comment.