Endurance’s $3.2 billion hostile bid for Aspen Insurance Holdings took another nasty turn on April 21.

Endurance’s chief financial officer asserted in a blunt statement that the continued resistance of Aspen board against joining forces is shortsighted and ignores shareholders’ best interests.

On Sunday, Aspen elaborated on its rejection of the offer from Endurance Specialty Holdings in a letter to its shareholders. Aspen’s board and company executives rejected the offer, in part, arguing that the proposed buyout would contribute to a loss of business. Aspen, in its shareholder letter, also alleged that Endurance had not adequately disclosed details about $1.05 billion in outside investment that is funding its M&A proposal.

Endurance didn’t mince words in response.

“Having already rejected our proposal, Apsen’s defensive statement simply repeats inaccurate characterizations and ignores the plain fact that we are offering shareholders significant value for their shares and the opportunity to participate in a larger, superior organization going forward,” Endurance CFO Michael McGuire said in the company’s statement. “This is another clear sign of an entrenched board and management that is not aligned with shareholder interests.”

Endurance said its offer includes “an equity commitment from industry-leading institutional investors” to fund part of the deal. It also asserts that “the combined company will have greater scale and market presence that will create expanded opportunities,” and “in the face of that, assertions about cultural issues and dis-synergies impeding the operation of the combined company are unfounded.”

McGuire added that Endurance will keep plowing ahead and remains “fully committed to delivering our highly attractive premium to Aspen shareholders.” He asserted that Endurance “will continue to take the steps necessary to make sure Aspen shareholders have the opportunity to realize a significant premium for their shares, even in the face of the misguided resistance of Aspen’s board.”

If the deal goes through, it would combine two of the “Class of 2001” Bermuda specialty insurance and reinsurance companies, each of which was a part of the Bermuda wave of development following the World Trade Center attacks. The combined company would handle more than $5 billion of combined annual gross premiums written and have $5 billion of pro forma common shareholders equity.

Endurance announced its buyout proposal on April 14, after what it said has been repeated rebuffs from Aspen’s board since January to embrace “confidential and friendly discussions” about a buyout.

Aspen’s founders include 39 people who formerly worked for a Lloyd’s of London business known as Wellington, including Aspen CEO Chris O’Kane.