LONDON (AP) — The CEO of Barclays bank is being investigated by regulators for his attempts to unmask a whistleblower who had written anonymous letters raising concerns about a senior employee.

Jes Staley sought to identify the person but was told it was inappropriate to do so under rules protecting whistleblowers. Staley then sought again to identify the whistleblower, even using help from a U.S. law enforcement agency, but failed.

The bank said Monday that Staley had honestly, but mistakenly, believed that he had clearance to identify the whistleblower.

He now faces an official inquiry by the Financial Conduct Authority and Prudential Regulation Authority for his "individual conduct and senior manager responsibilities" related to the company's whistleblowing program.

The bank said Staley will face a written reprimand and a "very significant" adjustment in his pay. The amount will be determined once the official inquiries have concluded.

Barclays says the board first learned about the problem earlier this year "as a result of a concern raised by an employee" who questioned the effectiveness of the bank's whistleblowing policy.

It said it used an independent law firm to investigate the allegations and also notified authorities of the possible wrongdoing.

The bank says Staley explained his actions to the board. The statement says the board concluded that Staley "honestly but mistakenly" believed it was permissible to identify the author of the letter.

The bank and Staley will cooperate fully with the investigations. Staley says he accepts the board's conclusion and has apologized.