Brennan Linsley, File, Associated Press
In this Nov. 28, 2014, file photo, shoppers look for deals inside the Flatiron Crossing Mall, a Macerich property in Broomfield, Colo. Mall operator Simon Property boosted its hostile bid for rival Macerich 5 percent. Simon said, Friday, March 20, 2015, it is willing to pay $95.50 per share for Macerich, or about $16.8 billion, up from its previous offer of $91 per share, or $16 billion.

NEW YORK — Mall operator Simon Property boosted its hostile bid for rival Macerich by 5 percent to $16.8 billion and says that will be its best and final offer.

The deal would combine two of the largest U.S. shopping mall operators.

Simon set an April 1 deadline for Macerich to respond to the offer, or it will be withdrawn.

Shares of Macerich fell dropped more than 7 percent in morning trading Friday while Simon Property shares edged higher.

Simon said Friday that it is now offering to pay $95.50 per share for Macerich, up from its previous offer of $91 per share. The new offer is valued at $23.2 billion, when debt of about $6.4 billion is included.

Macerich rejected Simon's first bid, saying the deal undervalued the company. It also said it had "serious antitrust concerns" because of Simon's partnership with General Growth Properties Inc. "It is a concerted effort by the two largest companies in the industry to acquire the number three company," Macerich said earlier this week.

Simon Property Group Inc., an Indianapolis real estate investment trust, went hostile earlier this month in making its offer, saying that Macerich refused to negotiate a deal.

A representative for Macerich Co. did not immediately respond to a request for comment Friday about the new offer.

Simon owns or has interest in more than 325 properties around the world, mainly outlets and malls. Macerich Co., based in Santa Monica, California, is a real estate investment trust that owns 51 shopping centers around the country.

Shares of Macerich fell $7.09, or 7.6 percent, to $86.41 Friday morning. Simon shares rose $1.79, or 1 percent, to $193.89.