Facebook boss Mark Zuckerberg has said the social network "didn't do enough" to protect user data in a written statement to the US Congress.
Ahead of appearances before US Congress committees on Tuesday and Wednesday, Mr Zuckerberg said he took responsibility for recent Cambridge Analytica data scandal, as well as the platform's issues with fake news and abusive content.
Facebook has confirmed it believes up to 87 million people had their data harvested by the political consultancy via a personality quiz app.
"It's clear now that we didn't do enough to prevent these tools from being used for harm as well," Mr Zuckerberg's written statement said of the platform.
"That goes for fake news, foreign interference in elections, and hate speech, as well as developers and data privacy. We didn't take a broad enough view of our responsibility, and that was a big mistake. It was my mistake, and I'm sorry. I started Facebook, I run it, and I'm responsible for what happens here.
"So now we have to go through every part of our relationship with people and make sure we're taking a broad enough view of our responsibility."
The social network's founder and chief executive also said the site did not spot Russian propaganda and misinformation quickly enough.
He said the company now estimates around 126 million people may have seen content from the Internet Research Agency (IRA), a Russian propaganda organisation which generated around 80,000 Facebook posts over a two-year period.
"We were too slow to spot and respond to Russian interference, and we're working hard to get better," the statement read.
"Our sophistication in handling these threats is growing and improving quickly. We will continue working with the government to understand the full extent of Russian interference, and we will do our part not only to ensure the integrity of free and fair elections around the world, but also to give everyone a voice and to be a force for good in democracy everywhere."
However, the company is now using artificial intelligence (AI) tools to help more quickly identify and shut down fake accounts, Mr Zuckerberg's statement says.
"There's no question that we should have spotted Russian interference earlier, and we're working hard to make sure it doesn't happen again," he said, adding that tools have been "successfully deployed" ahead of recent elections in France, Germany and the US state of Alabama.
In the closing remarks of his submission, Mr Zuckerberg said Facebook users would remain a priority for the company.
"My top priority has always been our social mission of connecting people, building community and bringing the world closer together. Advertisers and developers will never take priority over that as long as I'm running Facebook," he said.