CHICAGO/ATLANTA (Reuters) - Private equity firm Sun Capital sent a letter to shareholders of Furniture Brands International Inc (FBN.N: Quote, Profile, Research) on Wednesday, questioning whether the furniture maker's board was acting in the best interest of all shareholders.

The letter was the latest salvo in Sun's proxy fight to gain three seats on Furniture Brands' board.

Furniture Brands' shares were up more than 3 percent in afternoon trading.

Sun Capital, which owns a 9.5 percent stake in Furniture Brands, said in February that it was willing to buy the maker of Thomasville, Henredon and other furniture lines for a "substantial premium" to the stock price then, which was $10.18.

Furniture Brands said last week that Sun had suggested a price of $13 to $15, but never followed up with a written offer.

Sun said in its letter on Wednesday that Furniture Brands' board has failed to appropriately consider two proposals to acquire the company.

"Instead, the current Board has, in our view, continued to pursue a failed strategy that has led to substantial stock price declines," the letter said.

Prior to Sun revealing its interest, Furniture Brands' stock had fallen by more than half its value in roughly two years.

St. Louis-based Furniture Brands has sold its business furniture division and formed an Asian unit to reduce costs and is closing stores and taking other steps as it tries to turn the company around.