"It is definitely a violation and we were slow to act", Dorsey said. "It violated the values of our company and of the country we love", Sandberg said in her written statement, which Facebook shared with Fortune.
Senator Mark Warner told the hearing that social media firms "were caught flat-footed by the brazen attacks on our election" and questioned whether Silicon Valley is capable of confronting the problem of foreign influence.
"Clearly, this problem is not going away", Burr said.
"The bad news, I'm afraid, is that there is a lot of work still to do".
TechCrunch also reported Dorsey agreed to set up a third-party civil rights audit, which would determine the platform's impact on minorities and other underrepresented communities.
Some 43% of people think tech companies favour liberal over conservative viewpoints and 72% think it's likely that social media companies intentionally censor political viewpoints they find objectionable.
And some of President Trump's strongest GOP allies in the House - Reps.
Moscow denies involvement, and Trump - backed by some of his fellow Republicans in Congress - has repeatedly dismissed investigations of the issue as a partisan witch hunt or hoax.
Conspiracy theorist Alex Jones held a press conference outside the Senate hearing room as the testimony began to criticize the social media companies for banning him and his website Infowars from their platforms.
Later in the day, Mr Dorsey faced a different hearing alone at the House Energy and Commerce Committee, focused on transparency and accountability, where he told lawmakers the company's number one priority was to ensure elections were not interfered with by foreign entities.
In prepared testimony released Tuesday before a Senate hearing Wednesday, Twitter chief executive officer Jack Dorsey says, "Twitter does not use political ideology to make any decisions, whether related to ranking content on our service or how we enforce our rules".
The social media executives underwent questioning before the Senate Intelligence Committee Wednesday. Google, however, risks having an empty chair at the hearing after cofounder Larry Page declined to appear.
It's both Dorsey and Sandberg's debut on Capitol Hill, and they're tasked with defending their companies and the sometimes malicious behavior that occurs on each medium.