The fight for Transatlantic Holdings Inc stepped up a notch yesterday after Bermuda-based Validus Holdings Ltd announced plans to replace Transatlantic’s board.

In a statement, Validus said the Transatlantic board had acted to “thwart” its unsolicited offer to buy the New York-based reinsurer and that it was filing papers with the Securities and Exchange Commission (SEC) to replace the Transatlantic board with three independent directors.

The move comes three months after Transatlantic agreed to a merger with Zug, Switzerland-based re/insurer Allied World Assurance Co Holdings AG. Validus and later Berkshire Hathaway Inc subsequently put in unsolicited bids for Transatlantic.

Validus has alleged that Transatlanic’s board set up “barriers designed to prevent Transatlantic from entering into good-faith discussions” about its “superior” offer, including adopting a “poison pill” strategy and entering into litigation against Validus.

Transatlantic had filed a plan with the SEC in July that would dilute the holdings of anyone who acquires more than 10 percent ownership. It also filed a federal lawsuit alleging that Validus made false and misleading statements in bid documents.

Transatlantic also amended corporate bylaws to give the Transatlantic board more control over stockholder meetings, Validus said.

In the filing, Validus nominated three directors to replace the Transatlantic board Raymond Groth, an adjunct professor of business administration at The Fuqua School of Business at Duke University in Durham, North Carolina, Paul Haggis, the chairman of the Alberta, a Canada-based private equity fund of funds manager Alberta Enterprise Corp, and Thomas Wajnert, a senior managing director of Reno, Nevada-based financial services advisory firm The Alta Group L.L.C.

Validus also said advisory firms Glass, Lewis & Co and Egan-Jones Proxy Services have issued reports recommending that Transatlantic stockholders vote against Allied World’s proposal when they meet on September 20. Another advisory firm, Institutional Shareholder Services Inc also made similar recommendation this week, citing the emergence of competing bids for Transatlantic.

All three deals to acquire Transatlantic were valued at more than $3 billion when they were announced, but have fluctuated due to the recent stock market turbulence.