Chief executives and other high-level corporate officers are seeking additional security protection after the brazen slaying of UnitedHealthcare's chief executive officer in New York, according to a top risk management firm.

"We had CEOs and other executive level and board members reaching out to us all throughout yesterday and today to increase their own executive protection, their own personal security around the clock, 24/7," said Matthew Dumpert, managing director at Kroll Enterprise Security Risk Management.

"An executive is the face of the organization," he said in an interview. "A CEO is the lightning rod that attracts the ire regardless of the product or services sold."

The killing of UnitedHealthcare CEO Brian Thompson occurred amid an increase in threats to people in the heath-care industry.

"The ire and the animosity that our front-line health-care workers experience every day in the hospital in the critical care environment does extend to the insurance industry to a degree," said Dumpert. "And it's because of a lot of those same red-flag indicators of potential violence."

Thompson's company, a division of UnitedHealth Group, is the largest payer of health insurance benefits in the United States.

Police believe the gunman who fatally shot the 50-year-old Thompson on Wednesday morning outside a midtown Manhattan hotel targeted him for some unknown reason as Thompson walked to a UnitedHealth Group investors meeting unaccompanied by any security.

But there was immediate public speculation after the slaying that Thompson had been shot in connection with his company's relatively high rate of denial of beneficiaries' health-care claims.

Bullet casings found at the shooting scene carried the words "deny," "defend" and "depose," a possible reference to the title of a 2010 book about insurance companies denying claims benefits. The gunman remained at large as of Thursday afternoon.

Chris Pearson, CEO of BlackCloak, which provides private digital security for C-suite executives and their families, said Thompson's killing appears unprecedented in recent U.S. history.

"The loss of life here ... the impact of family, impact of company, impact of friends, is just overwhelming, absolutely overwhelming," Pearson said in an interview with CNBC.

"I personally have not seen anything like this," he said. "I don't think we've seen anything to this level in the United States."

Pearson said Thompson's slaying could affect security arrangements for executives and how protection firms evaluate their risks at public events, board meetings, conferences and speaking engagements "where their physical presence is known or likely to be anticipated."

"I think that's really the new risk that has to be dimensioned today," he said.

Thompson did not have a dedicated security detail, in contrast to some other executives in the health-insurance sector.

Dumpert said the companies who have sought extra protection from Kroll in the past 36 hours range across industry sectors.

Twenty percent of S&P 500 companies list some kind of security benefit for chief executives, according to recent proxy statements.

A CNBC analysis of data from market intelligence firm AlphaSense found this is around 7 percentage points higher than a decade ago.

UnitedHealth's two most recent proxy statements do not show any current or former executives receiving regular company-funded security services.

Most companies disclose private jet services for executives' security if it is provided.

In health care, Cigna, Humana and UHG disclose such benefits in their proxy statements for their CEOs.

Vaccine makers Moderna and Pfizer in 2023 revealed that they each had spent upwards of $1 million on executive security for their CEOs.

In a proxy filing two days before the shooting, Walgreens said it is providing home security services for the pharmacy company's CEO, Tim Wentworth.

"To protect Mr. Wentworth against possible security threats to him and his family members, the company requires that Mr. Wentworth accept such personal security protection while he serves as CEO," Walgreens said in its filing.

"The company believes that the costs of this security were appropriate and necessary, particularly in light of the heightened risk environment in the retail pharmacy industry," said Walgreens.

CVS Health disclosed in a proxy statement in 2023 that it required then-CEO Karen Lynch to use its corporate aircraft "pursuant to an executive security program," for both business and personal travel.

"Similar to our approach to aircraft, Ms. Lynch uses a corporate driver for travel as part of our executive security program in order to minimize and more efficiently use travel time, protect the confidentiality of travel and our business, and enhance the CEO's personal security," that filing said.

Lynch was replaced as CEO in October by David Joyner.

— Additional reporting by CNBC's Nick Wells.