OTTAWA -- Facebook founder Mark Zuckerberg made a public apology Wednesday for his company's handling of users' personal information -- including more than 620,000 Canadians -- as the social media giant faced a growing international uproar over the questionable use of personal data for political purposes.

The company estimates 622,161 users in Canada had their data improperly shared with Cambridge Analytica through apps used by themselves or their friends.

Overall, Facebook says that 87 million of its users worldwide were affected -- significantly more than the 50 million originally believed to be affected -- with nearly 82 per cent of them believed to be located in the United States.

The company said those affected will find out Monday if their information was improperly shared with Cambridge Analytica.

Zuckerberg said the privacy breach showed his company didn't take seriously its responsibility towards users "and that was a huge mistake."

"It was my mistake. 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," he said during an afternoon conference call with reporters.

"It's not enough to just connect people. We have to make sure those connections are positive and that they bring people closer together."

Canada's privacy commissioner said he wasn't surprised at the magnitude of the number of Canadians affected. Speaking in Toronto, Daniel Therrien said the figure will work into his ongoing investigation about the data breach and whether there were any violations of federal privacy laws.

Facebook is facing its worst privacy scandal ever in the wake of allegations that Cambridge Analytica used data collected without users' authorization to help Donald Trump's 2016 presidential campaign and possibly other elections. Policy makers in Canada and other countries are now wrestling with how to respond to the spread of "fake news" on social media platforms like Facebook, which announced Wednesday it had also shut down accounts and pages linked to a Russian agency accused of online meddling in foreign elections.

Zuckerberg said the company would bring to 20,000 the number of workers dedicated to battling "fake news," as he apologized for initially dismissing the notion that the misinformation campaign had any impact on election outcomes.

The social media giant plans to restrict data access on its platforms, which includes Instagram, to better protect users' information. Facebook will disable a feature that let anyone search Facebook for a user with their email or phone number, saying in a post that "malicious actors" had used the tool to scrape personal data of most users on Facebook. And starting Monday, it will show people which apps use their Facebook information.

Zuckerberg is set to testify next week before a U.S. congressional committee, and he said top executives at the company would be dispatched to other countries wanting to hold government hearings on the scandal.

Canada's acting minister for democratic institutions called Facebook's admission of the scope of the breach "deeply concerning."

"While Facebook has begun to take initial steps to address these issues, it is clear that much more needs to be done," Scott Brison said in a statement.

Brison has said he'd be open to strengthening federal privacy laws, which don't currently apply to political parties. And Zuckerberg appeared open to further regulation in a sector that has so far shied away from government oversight.

International experts in the national capital Wednesday to talk about the issue of "fake news" said the Liberals needed to enact stronger privacy laws to better regulate how social media giants use Canadians' personal information.

"Since there are insufficient limits on what you can do with personal data, there is no countervailing force," said David Carroll, an American academic who is suing Cambridge Analytica in the U.K. to gain access to his data.

"We need to realize that privacy legislation will weaken the behemoths in a healthy way."

Other options put forward included greater transparency for online advertising that would enable users to easily learn who paid for a Facebook ad, how much they spent, how many people viewed it and why the ad targeted the user. Ben Scott, a former adviser in the State Department, said countries should look for ways to restrict the use of personal data for political targeting to avoid the kind of dirty tricks campaigns Cambridge Analytica is accused of conducting.

Sue Gardner, former executive director of Wikimedia Foundation, said there is general opposition south of the border to government regulations in the sector, with a belief that government involvement would make matters worse. Instead, recommendations in the U.S. centre around self-regulation.

"Those are massively insufficient for the scope of the problem," she said.

-- With files from Andy Blatchford in Ottawa and Dave Paddon in Toronto