Facebook CEO Mark Zuckerberg is taking personal responsibility for letting third parties access Facebook user data without permission, and says the company will embark on a three-year push to prevent it from happening in the future.

"I started this place, I run it," Zuckerberg said during a call with reporters on Wednesday. "I'm responsible for what happened here."

No one has been fired at Facebook due to the Cambridge Analytica data leak scandal, he revealed. But he admitted the company did not do enough to focus on preventing abuse and minimized the impact of its platforms, calling the lack of action "a huge mistake, my mistake."

He added, "I'm going to do the best job running it going forward, but I'm not going to throw anyone under the bus."

Facebook has been under heavy scrutiny over its use of user data, especially after evidence of Russian interference through advertising during the 2016 U.S. presidential election was discovered. In March, The Guardian and the New York Times reported consulting firm Cambridge Analytica used personal data which was obtained improperly through a quiz app to find potential President Donald Trump voters.

The process to safeguard Facebook is a multi-year effort, Zuckerberg said adding the company will focus on a three-year push but is committed to on-going work. While it may incrementally get better over time, Zuckerberg doesn't expect it will be fixed anytime soon "given how complex Facebook is and how many systems there are and how we have to rethink our relationship with people."

Facebook has 15,000 people working on security and reviewing content, and will have 20,000 by the end of the year, Zuckerberg said.