Uber's CEO Travis Travis Kalanick has sent a company-wide email responding to a blog written by former employee Susan Fowler alleging workplace sexual harassment, according to a copy posted on Twitter on late Monday in the U.S. and confirmed by CNBC, announcing a review led by former U.S. Attorney General Eric Holder along with a partner at the law firm of Covington & Burling.

The email also said the Uber board member Arianna Huffington, and recently hired Human Resources head Liane Hornsey, as well as the company's associate general counsel Angela Padilla will join the probe. Among the allegations in Fowler's blog, was a pattern of sexual harassment and gender bias during her roughly year-long employment at the company, including via the internal messaging system.

"On my first official day rotating on the team, my new manager sent me a string of messages over company chat. He was in an open relationship, he said, and his girlfriend was having an easy time finding new partners but he wasn't. He was trying to stay out of trouble at work, he said, but he couldn't help getting in trouble, because he was looking for women to have sex with."

Kalanick's email did not go into details about the claims by Fowler, but did indirectly address gender diversity at the firm.

"There have been many questions about the gender diversity of Uber's technology teams," Kalanick wrote in the email. "If you look across our engineering, product management, and scientist roles, 15.1 percent of employees are women and this has not changed substantially in the last year. As points of reference, Facebook is at 17 percent, Google at 19 percent and Twitter is at 15 percent."

[Editor's note: Uber issued revisions to Kalanick's statement on the other companies' diversity statistics. Those changes have made to the above quote and below reproduction. The original version of his note under-reported the percentage of female employees at Google and Twitter.]

He added that the review would be conducted in "short order."