Germany's justice minister voiced scepticism Monday about Facebook's willingness to reform, speaking after a Berlin meeting with its founder Mark Zuckerberg.
"For the past year, Mark Zuckerberg has been speaking about Facebook's responsibility to society, democracy and the privacy of more than two billion people," said Katarina Barley in a statement.
"But we haven't quite seen it yet. Facebook's behaviour has cost it a lot of trust."
Facebook has drawn fire on several fronts - for allowing users to spread hate speech and even live-stream the bloody New Zealand mosque attacks, to letting foreign powers meddle in politics to broad concerns over its collection of personal user data.
Germany has for years vocally complained about Facebook allowing far-right groups and other extremists to spread hate speech that breaches German sedition laws.
Zuckerberg last Saturday called for governments to play a "more active role" in regulating the Internet, urging more countries to adopt versions of sweeping European rules aimed at safeguarding user privacy.
The US Internet giants have long resisted government intervention, but the leading social network reversed course amid growing calls for regulation, in an apparent bid to help steer the debate.
Addressing privacy protection, Zuckerberg said he would support more countries adopting rules in line with the European Union's sweeping General Data Protection Regulation.
Barley, after talks with Zuckerberg, remained critical.
"Facebook already has every opportunity to guarantee the highest level of data protection, regardless of state regulation, for its users," she said.
"Instead, barely a month goes by without a new security scandal."
She also criticised Zuckerberg's plan to merge the technical infrastructure behind Facebook's WhatsApp and Messenger chat services and Instagram's communications feature.
Barley said the plan was contrary to earlier announcements and raises "very significant antitrust and data protection issues".