Barclays CEO Jes Staley is counting the cost of attempting to identify a whistleblower in 2016.

UK financial regulators announced Friday that Staley had been fined £642,430 ($870,000) after he "failed to act with due skill, care and diligence."

In addition, Barclays said it would claw back £500,000 ($680,000) of Staley's 2016 pay over the incident. The CEO made £4.2 million ($5.7 million) that year, including bonus, benefits and pension payments.

"Staley breached the standard of care required and expected of a chief executive in a way that risked undermining confidence in Barclays' whistleblowing procedures," said Mark Steward, executive director of enforcement and market oversight at the Financial Conduct Authority.

In addition to the fine, Barclays (BCS) will be required to report each year on how it handles whistleblowing, the regulators said.

Staley said in a statement that he accepted the conclusions of the regulators.

"I have consistently acknowledged that my personal involvement in this matter was inappropriate, and I have apologized for mistakes which I made," he said.

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The American banking executive admitted last year that he had "made a mistake" by attempting to find out who authored an anonymous letter that raised concerns about a senior Barclays employee.

"I should have left the organization to handle it," Staley said in 2017, while announcing that he would not resign from his position.

The bank's board and an external law firm concluded following an initial investigation that Staley had "honestly, but mistakenly believed that it was permissible to identify the author of the letter."

Staley is still being investigated by US authorities over the incident. Barclays said Friday it continues to cooperate with that investigation.

-- CNN's Alanna Petroff contributed to this report.