Shares of Facebook and Twitter both fell as their top executives testified before the US House of Representatives, defending their companies against what lawmakers and others have called a failure to combat foreign efforts aimed at influencing US politics.

Facebooks shares fell 1.6 per cent and Twitters by 5.2 per cent, with shares in other tech firms including Alphabet and Snap also impacted by the hearings.

The hearings focused on whether the tech firms had reacted appropriately when evidence of election tampering by foreign agents was discovered, and what they are doing to prevent similar occurrences in the future.

During their testimony Sheryl Sandberg, chief operating officer at Facebook, admitted that the social network was “too slow” to act on election interference, while Jack Dorsey, CEO of Twitter, said that the company was “unprepared and ill-equipped” for the “weaponisation” of the political discourse.

“With the benefit of hindsight, it is obvious that serious mistakes were made by both Facebook and Twitter,” said Democratic Senator Mark Warner. “You, like the US government, were caught flat-footed by the brazen attacks on our election. Even after the election, you were reluctant to admit there was a problem.”

Senator Warner went on to hint that new regulations could be introduced to govern social networks, telling the hearing that the “era of the wild west in social media is coming to an end”.

Dorsey and Sandberg were asked a wide variety of questions during the hearings, including whether it was possible to indicate whether Twitter accounts were run by humans or bots, whether users could be notified that they had engaged with fake accounts following their removal, and if a US citizen “intentionally spreading false information” would violate Facebooks community standards. Sandberg said that Facebook did not want to become the “arbiter of truth” and was working with third-party fact-checkers to identify misinformation.

Despite being invited, no representatives from Alphabet or Google appeared at the Senate Intelligence Committee hearing. During the hearings opening statements, Senator Warner said he was “deeply disappointed” the Google “chose not to send its own top corporate leadership”. An empty chair was left for the firm during the hearings.

Elsewhere in Washington, the Justice Department has said that it has convened a meeting with state attorneys general to discuss concerns that social media platforms were “intentionally stifling the free exchange of ideas”. During a hearing, Representative Greg Walden, chairman of the House Energy and Commerce Committee, claimed that Twitter had made “mistakes” that minimised Republican presence on the platform.

“Multiple members of Congress and the chairwoman of the Republican Party have seen their Twitter presences temporarily minimised in recent months, dur to what you have claimed was a mistake in the algorithm.”

During his opening statement, Dorsey said that Twitter didnt take political positions, and that “impartiality is our guiding principle”.

President Trump, in an interview with conservative outlet The Daily Caller, claimed that social media companies were interfering in the upcoming US mid-term elections, saying that social media firms are “super liberal”. He offered no evidence to support his claims.