San Francisco: Facebook Inc Chief Executive Mark Zuckerberg said on Wednesday that his company made mistakes in how it handled data belonging to 50 million of its users and promised tougher steps to restrict developers’ access to such information.

The world’s largest social media network is facing growing government scrutiny in Europe and the United States about a whistleblower’s allegations that London-based political consultancy Cambridge Analytica improperly accessed user information to build profiles on American voters which were later used to help elect US President Donald Trump in 2016.

Zuckerberg, in his first public comments since the scandal erupted at the weekend, said in a post on Facebook that the company ‘made mistakes, there’s more to do, and we need to step up and do it.’

He did not elaborate on what the mistakes were, but he said the social network plans to conduct an investigation of apps on its platform, restrict developer access to data, and give members a tool that lets them more easily disable access to their Facebook data.

His plans did not represent a big reduction of advertisers’ ability to use Facebook data, which is the company’s lifeblood.

Zuckerberg later told CNN, ‘This was a major breach of trust. I’m really sorry this happened. We have a basic responsibility to protect people’s data.’

He told CNN that Facebook was committed to stopping interference in the US midterm election in November and elections in India and Brazil.

Zuckerberg said he was open to additional government regulation and happy to testify before the US Congress if he was the right person.

‘I’m not sure we shouldn’t be regulated,’ he said. ‘I actually think the question is more what is the right regulation rather than yes or no, should it be regulated? ... People should know who is buying the ads that they see on Facebook.’

Facebook shares pared gains on Wednesday after Zuckerberg’s post, closing up 0.7 percent. The company has lost more than $45 billion of its stock market value over the past three days on investor fears that any failure by big tech firms to protect personal data could deter advertisers and users and invite tougher regulation.

Facebook representatives including Deputy Chief Privacy Officer Rob Sherman met US congressional staff for nearly two hours on Wednesday and planned to continue meetings on Capitol Hill on Thursday. Facebook was unable to answer many questions, two aides who attended the briefing said.

Zuckerberg told the website Recode that fixes to protect users’ data would cost ‘many millions of dollars.’

The whistleblower who launched the scandal, Christopher Wylie, formerly of Cambridge Analytica, said in a tweet that he had accepted invitations to testify before US and UK lawmakers.

The German government said Facebook must explain whether the personal data of the country’s 30 million users were protected from unlawful use by third parties, according to a report in the Funke group of German regional newspapers.