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A senior executive at the ride-hailing firm Uber has resigned, following an investigation into how she handled allegations of racial discrimination at the firm.

Liane Hornsey was head of Uber's human resources department, with the title of chief people officer.

She had been in the role for 18 months.

Her departure comes just a year after the firm's founder, Travis Kalanick, left under a cloud following reports of gender discrimination and harassment.

Since then, new chief executive Dara Khosrowshahi has focused on turning around the company's reputation and overhauling what some said had become a toxic corporate culture.

The departure of Ms Hornsey, who previously worked for Google, represents another setback for the firm.

Uber has also had to wrestle with licensing problems in major cities, including London, and has had to call a temporary halt to its driverless car programme following a fatality.

Analysis: Dave Lee, North America business reporter

At "new" Uber, in the post-Travis Kalanick age, they're taking no chances.

As head of HR, Liane Hornsey had survived Uber's well-publicised troubles, despite being at the helm of a firm with some famously deep-rooted people problems.

But now, time is apparently up. Officially the company isn't going into the details - but a source at the company confirmed to me the details in Reuters' report: that an investigation into how Ms Hornsey handled racial discrimination complaints was the reason she had to leave.

Liane Hornsey came to the company with quite a reputation. The former Googler was seen as a major coup, one of the most well-regarded names in tech industry HR. And Uber really needed her help - it was growing rapidly. It will now need to move on without her.

Anonymous whistleblowers at Uber have claimed Ms Hornsey systematically dismissed internal complaints of racial discrimination. They said reports to the firm's internal anonymous tip line were often left unresolved or dismissed, especially if they dealt with issues of race.

Unnamed employees also said Ms Hornsey had used discriminatory language and made derogatory comments about two fellow Uber executives.

Law firm Gibson Dunn carried out an investigation which substantiated some of the allegations made. A second investigation is expected.

Mr Khosrowshahi praised Ms Hornsey in an email to employees as "incredibly talented, creative and hard-working".

Neither he nor Ms Hornsey gave any reason for her departure.

Ms Hornsey, in a separate email to employees, said she realised her exit "comes a little out of the blue for some of you, but I have been thinking about this for a while".

Uber said the set of complaints over racial discrimination had been properly dealt with.

"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.