United Technologies Corp. forcefully rejected Honeywell International Inc.’s purchase offer as the companies traded public statements over the proposed $90 billion tie-up.

Honeywell’s $108-a-share bid this month “grossly undervalues” United Technologies, its chief executive officer said in an open letter filed Friday with the U.S. Securities and Exchange Commission. A deal would likely be blocked by antitrust regulators or require heavy divestitures, said CEO Gregory Hayes, reiterating similar comments he made this week.

“Putting aside the insurmountable regulatory risks, the proposal is not an attractive deal for UTC’s shareholders and does not reflect UTC’s strong long term outlook,” he said. United Technologies also released slides listing other deals blocked by regulators and detailing the opposition of customers including Boeing Co. and Airbus Group SE.

United Technologies declined 1.1 percent to $96.97 a share at 2:35 p.m. in New York following a brief halt before the company’s announcement. The stock is up 10 percent since Feb. 19, the last trading day before the Honeywell offer became public. Honeywell fell less than 1 percent to $103.51 Friday.

The United Technologies’ release was made a few hours after Honeywell released a 10-page presentation saying a tie-up would create $72 billion in combined shareholder value.

Honeywell Gambit

By publicizing its detailed accounting of the offer, Honeywell put pressure on United Technologies to reconsider a combination that would have annual revenue in excess of $90 billion, selling wares spanning jet engines, thermostats and elevators. Honeywell said in a statement that it released the slide show in response to investor inquiries.

The proposed combination would lead to cost savings of $3.5 billion in four years, according to the Honeywell slide show. The combined entity would raise $36 billion in debt, Honeywell said in the 10-page presentation, which it delivered to United Technologies executives on Feb. 19. The offer values United Technologies at about $90 billion excluding debt.

The transaction is “strongly worth pursuing,” Honeywell said in the presentation, which was made to Hayes and United Technologies Chairman Edward Kangas. Honeywell chief David Cote would serve as CEO and chairman of the resulting company, according to the proposal. The combination is a “compelling, transformational opportunity for both sets of shareholders,” Honeywell said.

Destroying Value

United Technologies on Friday put cost savings at about $2.5 billion and said the deal could destroy up to $7 billion of value because of divestitures and concessions to aerospace customers.

While a deal would be “messy,” it may work if Honeywell is willing to divest about $10 billion of assets, Peter Arment, an analyst at Sterne Agee CRT, said Friday in a note circulated before the Honeywell release. Honeywell may need to increase its offer to about $115 a share, he said.

The companies together would have operating margins of about 20 percent and annual cash flow of about $10 billion, which would allow for “rapid deleveraging” and flexibility for investment, the Honeywell presentation said.