Top officials from Facebook, Google and Twitter were grilled by US lawmakers on Thursday at a virtual hearing on foreign influence and election security ahead of the Nov. 3 presidential contest.

Leaders from Facebook Inc and Twitter Inc told the House of Representatives Intelligence Committee that they had not seen evidence of coordinated foreign interference in conversations about absentee voting or about recent protests on anti-racism and policing.

However, Twitter's director of global public policy strategy and development Nick Pickles said the company had seen a shift from platform manipulation to public tweets from state media and government accounts.

Democratic Representative Jim Himes pressed Facebook's head of security policy Nathaniel Gleicher on what the company was doing to deal with worries that its algorithm promotes polarization and anger.

"If every single American household is full of toxic, explosive gas, as I think it is today, all it takes is a match from Russia or from Iran or from North Korea or from China to set off a conflagration," said Himes.

Gleicher said Facebook's users did not want to see divisive content and the platform had refocused to emphasize content from friends and family.

The debate over content moderation has intensified in recent weeks as Twitter and Facebook diverged on how to handle inflammatory posts by President Donald Trump. Trump, in turn, has accused social media companies of censorship and called for the government to roll back liability protections for tech platforms.

Richard Salgado, director for law enforcement and information security Alphabet Inc's Google, faced accusations that the company's lack of transparency about content on its platform had allowed it to avoid the heat that other tech firms had drawn. Salgado said Google does provide transparency reports around advertising on the platform.