Simon Property Group Inc (SPG.N) offered to buy Macerich Co (MAC.N) for $14.39 billion in a deal that would join the No. 1 and No. 3 U.S. shopping mall owners.

The cash-and-stock offer follows multiple refusals by Macerich to discuss a possible deal, which has enterprise value of $22.4 billion including debt, Simon said on Monday.

Macerich shares rose as much as 7 percent to an 8-year high of $92.43, brushing past Simon's offer of $91 per share. Simon shares were flat at $180.61 in afternoon trading.

A combination of Indianapolis-based Simon and Santa Monica, California-based Macerich could boost their ability to negotiate leases with store owners at a time when mall operators are experiencing a fall in traffic as consumers take to shopping online, which is more convenient and often cheaper.

A deal would also help Simon, which has a market value of about $57 billion, expand in California and Arizona, where Macerich's portfolio of about 53 shopping centers is concentrated.

Simon, led by former investment banker David Simon, has been aggressive its takeover strategy.

In 2010, the company tried to buy General Growth Properties Inc (GGP.N), now the No. 2 mall owner, with a $10 billion offer.

Simon disclosed a 3.6 percent stake in Macerich in November, seen by many at the time as a precursor to a bid. Up to Friday's close, Macerich's stock had risen 17.7 percent since Simon disclosed its stake.

The offer, which is at a premium of 4.9 percent to Macerich's Friday close, will be 50 percent in cash and 50 percent in Simon common stock.

"Considering the substantial benefits our offer provides, we are confident that, given the opportunity, Macerich's shareholders would accept our proposal," David Simon, Simon's chairman and chief executive, said in a statement.

Macerich, led by co-founder Chairman and Chief Executive Art Coppola, said it would review Simon's proposal.

The equity value of the deal is based on Macerich's 158.16 million shares outstanding as of Feb. 20.

Simon said it did not expect any legal hurdles to the proposed transaction, which would add to its funds from operations (FFO) immediately.

The company said it had agreed to sell selected Macerich assets to General Growth Properties.

BofA Merrill Lynch is the financial adviser to Simon and Latham & Watkins, LLP is legal counsel.