Two early Uber investors have slammed the ride-hailing company for allegedly failing to curb its "destructive culture" and history of "toxic patterns" following recent allegations of sexual harassment and sexism. In an open letter published on Medium, Mitch and Freada Kapor criticised the company for its culture of "disrespect, exclusionary cliques, lack of diversity, and tolerance for bullying and harassment of every form".

"As early investors in Uber, starting in 2010, we have tried for years to work behind the scenes to exert a constructive influence on company culture," they wrote. "We are speaking up now because we are disappointed and frustrated; we feel we have hit a dead end in trying to influence the company quietly from the inside."

The Kapors' statement comes after former Uber engineer Susan Fowler published a scathing blog post saying she was sexually harassed by her direct supervisor on her first day and immediately reported it to the human resources department. However, the HR department did not punish the manager, saying he was a "high performer".

Fowler also described a series of other incidents experienced during her one year at Uber involving alleged sexism, workplace abuse and an ongoing "game-of-thrones political war" within the upper management.

Shortly after Fowler's post went viral, Uber CEO Travis Kalanick called for an "urgent investigation" into the allegations saying the incidents described by Fowler were "abhorrent". Uber hired former US attorney general Eric Holder and Tammy Albarran - partners at law firm Covington and Burling - to lead the independent investigation.

Uber board member Arianna Huffington also met Kalanick and Uber's new chief resources officer Liane Hornsey in an "all-hands meeting" at Uber's offices in San Francisco.

The Kapors, however, criticised the company's response to the allegations saying they were "disappointed to see that Uber has selected a team of insiders to investigate its destructive culture and make recommendations for change".

"Eric Holder has been working on behalf of Uber since at least last June, when he and his firm were hired to advocate on behalf of Uber to lawmakers concerning using fingerprints as part of background checks on drivers," they wrote. "Arianna Huffington has held a board seat for about a year and is deeply invested in the company weathering the PR crisis. As the company's Chief Human Resources officer, Liane Hornsey reports to Travis' executive team."

"This group is not set up to come up with an accurate analysis of the culture and a tough set of recommendations," they continued. "To us, this decision is yet another example of Uber's continued unwillingness to be open, transparent, and direct."

Two early Uber investors have criticised the company for its "aggressive" and "toxic" culture. Justin Sullivan/Getty Images

Holder and Albarran released a statement in response to the Kapors' letter, Reuters reports, saying: "We will be thorough, impartial, and we are conducting this review with the highest degree of integrity and professionalism."

The Kapors, who are also diversity advocates and run the Kapor Center in Oakland to promote diversity and inclusion in the tech sector, said Uber has had "countless opportunities to do the right thing". They are also the first investors to publicly criticise the company in the wake of its latest controversy in recent months.

"We are concerned that the company will try to manage its way past this crisis and then go back to business as usual," they wrote. "As investors, we certainly want to see Uber succeed, but success must be measured in more than just financial returns. Uber's response to this particular crisis will be defining for the company, so the stakes are high to get it right."