ABC News

Burr, the chair of the Senate Intelligence Committee — which is leading congressional investigations into Russian interference in the 2016 presidential election — gave a closing statement at the hearing.

"The Russians conducted a structured influence campaign using US-based social media platforms and others to target the American people using divisive issues such as race, immigration, and sexual orientation," said Burr, a Republican.

"That campaign is still active today."

Experts and intelligence officials have warned that the US — including technology companies — is not doing enough to fight the threat of social media manipulation.