(Reuters) — Uber Technologies Inc.'s Chief People Officer Liane Hornsey resigned in an email to staff on Tuesday, following an investigation into how she handled allegations of racial discrimination at the ride-hailing firm.

The resignation comes after Reuters contacted Uber on Monday about the previously unreported investigation into accusations from anonymous whistleblowers that Ms. Hornsey had systematically dismissed internal complaints of racial discrimination.

Ms. Hornsey is head of Uber's human resources department and one of the firm's top spokespeople on diversity and discrimination issues. She had been in the role for about 18 months, as the company was rocked by claims of widespread issues of gender discrimination and sexual harassment.

The allegations raise questions about Chief Executive Dara Khosrowshahi's efforts to change the toxic culture of the firm after he took over in August last year from former CEO Travis Kalanick following a series of scandals.

Mr. Khosrowshahi praised Ms. Hornsey in an email to employees, which was seen by Reuters, as "incredibly talented, creative and hard-working." He gave no reason for her departure.

Ms. Hornsey acknowledged in a separate email to her team at Uber, also seen by Reuters, that her exit "comes a little out of the blue for some of you, but I have been thinking about this for a while."

She also gave no reason for her resignation and has not responded to requests for comment about the investigation.

The allegations against her and Uber's human resources department more broadly were made by an anonymous group that claims to be Uber employees of color, members of the group told Reuters.

They alleged Ms. Hornsey had used discriminatory language and made derogatory comments about Uber Global Head of Diversity and Inclusion Bernard Coleman, and had denigrated and threatened former Uber executive Bozoma Saint John, who left the company in June.

"This person ultimately was the reason behind (Saint John's) departure from Uber," the anonymous employees said in an email, referring to Ms. Hornsey.

Ms. Saint John joined Uber from Apple Inc. in June 2017 but left only a year later to join Endeavor, the parent company of several talent agencies. She declined to comment, telling Reuters by phone: "I don't have anything to say about my experience there."

Mr. Coleman, who came to Uber in 2017 after serving as the chief diversity and human resources officer of Hillary Clinton's 2016 presidential campaign, also declined to comment.

Some of the allegations were substantiated, investigators from law firm Gibson Dunn told the employees in a May 15 email that was seen by Reuters.

It is not clear which of the allegations were substantiated, but the investigators shared their "thoughts regarding several options to address concerns regarding Ms. Hornsey" with Mr. Khosrowshahi, they wrote in the email.

The investigators added that they were commencing another investigation after receiving a complaint from another anonymous Uber employee regarding "allegations that appear to relate in some ways."

Unresolved complaints

The complaints against Ms. Hornsey come about a year after Uber was embroiled in widespread allegations of gender discrimination and sexual harassment, triggering an investigation by former U.S Attorney General Eric Holder and ultimately Mr. Kalanick's resignation.

Uber in March agreed to pay $10 million to settle a proposed class-action lawsuit alleging discrimination against more than 400 women and minorities brought by three women engineers. One of the women removed herself from the class-action and sued the company in May alleging discrimination based on gender and race.

The employees behind the latest allegations said complaints filed to Uber’s anonymous tip line often were left unresolved or were dismissed, especially if they dealt with issues of race.

They also accused the company of ignoring a board-approved recommendation by Mr. Holder that its chief diversity officer report directly to the CEO or COO.

Uber told Reuters in a statement that the latest complaints had been properly investigated.

"We are confident that the investigation was conducted in an unbiased, thorough and credible manner, and that the conclusions of the investigation were addressed appropriately," it said.