He was testifying over a recent data breach involving Cambridge Analytica
A US Senate Committee has seen Facebook CEO Mark Zuckerberg answering questions about a recent data breach.
He was testifying before a joint hearing of the Senate Judiciary and Commerce Committees in relation to Cambridge Analytica.
It began with opening speeches by senior senators on the 44-person panel.
Mr Zuckerberg than gave his opening speech, in which he said: "We didn't take a broad enough view of our responsibility and that was a big mistake - and it was my mistake and I'm sorry.
"I started Facebook, I run it and I'm responsible for what happens here".
Joint Senate Judiciary and Commerce committee Hearing with Facebook CEO, Mark Zuckerberg pic.twitter.com/x3RXVBMsYW— Senator John Cornyn (@JohnCornyn) April 10, 2018
More than 44,000 people in Ireland may have had their data improperly shared with Cambridge Analytica, the social network has said.
Mr Zuckerberg has previously admitted the company "didn't do enough" to prevent abuse of its platform.
It has also revealed more than 87 million people around the world may have had their data improperly shared with Cambridge Analytica - significantly more than earlier estimates of 50 million.
Facebook has previously accused an academic, Dr Aleksandr Kogan, of violating its terms by passing on data from a personality test app - thisisyourdigitallife - to the UK-based political consultancy firm.
According to the social network, the vast majority of accounts - 70 million - that may have been affected belong to people in the US.
In one instance during the Senate hearing, Senator Richard Blumenthal held up cut-outs of the terms of service that Mr Kogan provided to Facebook.
"In fact, Facebook was on notice that he could sell that user information - have you seen those terms of service before?".
Mr Zuckerberg replied: "I have not".
Asked who was responsible for those terms of service, Mr Zuckerberg said: "Our app review team would be responsible for that".
Asked by Senator Blumenthal if anyone had been fired on that app review team, Mr Zuckerberg said: "Senator, not because of this".
But the Facebook CEO said they "should have been aware that this app developer submitted a term that was in conflict with the rules of the platform."
Senator Blumenthal then suggested: "What happened here was, in effect, willful blindness - it was heedless and reckless which in fact amounted to a violation of the FTC Consent Decree - would you agree?"
"No, Senator", Mr Zuckerberg replied.
Before attending the US Senate hearing, Mr Zukerberg posted on his Facebook page: "I’m going to testify in front of the Senate about how Facebook needs to take a broader view of our responsibility - not just to build tools, but to make sure those tools are used for good.
"I will do everything I can to make Facebook a place where everyone can stay closer with the people they care about, and to make sure it's a positive force in the world."
The revelations prompted a number of international investigations.
Cambridge Analytica - which is known for its work for political groups, including Donald Trump's presidential campaign - has said it did not receive data from 87 million people, and insisted it immediately deleted data when it was informed data may have been improperly obtained.
It also claims none of the data was used during the 2016 US election.
The European Parliament has invited Mr Zuckerberg to appear before it to answer questions.
President Antonio Tajani said he invited Mr Zuckerberg to "clarify before the representatives of 500 million Europeans that personal data is not being used to manipulate democracy."
The Oireachtas Communications Committee is also set to call Facebook and the Data Protection Commissioner to appear before it over the scandal.
The Green Party said the committee has agreed to its request. It is expected the committee will consider the issue later this month.