General Growth Properties Inc., the second-largest U.S. shopping-mall owner, rejected investor Bill Ackman’s request to put itself up for sale and said it will remain independent.

“The board has unanimously determined that the best value for all shareholders will be achieved by GGP continuing to execute on its well-conceived business plan,” Sandeep Mathrani, General Growth’s CEO, said in a letter to Ackman, founder of Pershing Square Capital Management LP. The letter was filed Monday with the U.S. Securities and Exchange Commission.

Pershing Square, General Growth’s No. 2 shareholder, first urged the retail landlord on Aug. 23 to form a special committee to consider selling the company. Ackman said at the time that Simon Property Group Inc. was interested in buying its smaller competitor. General Growth should “initiate negotiations with Simon promptly,” he said in a letter filed Aug. 27 with the SEC.

General Growth exited bankruptcy protection in November 2010 following a takeover battle between Indianapolis-based Simon and an investor group that included Pershing Square and Brookfield Asset Management Inc. General Growth filed for bankruptcy in 2009 after weighing itself down with $27 billion in debt that it was unable to refinance because of the financial crisis and collapse of the commercial mortgage-backed securities market.

Brookfield, General Growth’s largest shareholder, “has been very clear that they have no interest of any kind in buying the rest of General Growth or letting someone else buy General Growth,” Rich Moore, an analyst at RBC Capital Markets in Solon, Ohio, said. “General Growth feels the same way. They don’t want to be sold to anybody. The only guy who wants all this to happen really is Bill Ackman over at Pershing because he wants the stock price to go up.”

Moore has a sector-perform rating on General Growth shares, the equivalent of a hold.

An e-mail to Ackman and a telephone message left at his New York office weren’t immediately returned. A message left for Les Morris, a spokesman for Simon, also wasn’t immediately returned.

General Growth’s chairman is J. Bruce Flatt, CEO of Toronto-based Brookfield, which has a stake of about 42 percent in General Growth. Ackman said last month that Brookfield had also expressed interest in taking over the mall owner. Following Ackman’s disclosure, Brookfield said it wasn’t trying to buy General Growth nor did it want to sell its stake in the company.

“We agree with the position unanimously taken by GGP’s board to have GGP continue to execute on its business plan,” Flatt said Monday in a letter to General Growth’s board and shareholders. “GGP is currently performing extremely well and we believe GGP is positioned for superior growth over the next five years versus any comparable retail mall investment.”

Simon had discussed paying 0.1765 of a Simon share for each General Growth share, according to Ackman. That would value General Growth at $27.57 a share, based on Simon’s closing price Monday.

That would have given General Growth a higher per-share value than Simon’s proposed takeover from more than two years ago. Simon said in May 2010 that it offered $20 a share for its competitor, which was under bankruptcy protection at the time.

General Growth owns or has stakes in 149 regional shopping malls with about 141 million square feet of leasable space in the U.S. and Brazil.