U.S. lawmakers bombarded top executives of Facebook, Google and Twitter with questions for some six hours in a virtual hearing on Thursday, blaming their platforms for political extremism, vaccine bashing and more, while promising new regulations to eliminate online disinformation.

"Your business model itself has become the problem and the time for self-regulation is over. It's time we legislate to hold you accountable," said Democratic Representative Frank Pallone, chair of the Energy and Commerce committee.

Democrats slammed the platforms for failing to stem misinformation about COVID-19 vaccines and incitement ahead of the January 6 Capitol Riot launched by Trump supporters in an attempt to violently overturn the election results.

Republican Representative Bob Latta accused the firms of operating "in a vague and biased manner, with little to no accountability," relying on a law giving them a "shield" against liability for content posted by others.

The liability shield is known as Section 230 of the Communications Decency Act, which provides immunity for online platforms from users' content. Lawmakers said they would introduce their own proposals to reform Section 230.

"The regulation that we seek should not attempt to limit constitutionally protected freedom of speech, but it must hold platforms accountable when they are used to incite violence and hatred or as in the case of the COVID-19 pandemic, spread misinformation that costs thousands of lives," said Democratic Representative Jan Schakowsky.

"People want to use your services, but they suspect your coders are designing what they think we should see and hear," said Republican Gus Bilirakis.

Jack Dorsey of Twitter, Sundar Pichai of Google, and Mark Zuckerberg of Facebook were also blamed for drug abuse, teen suicides, hate and illegal immigration on their platforms.

The three companies said they have taken steps to curb misinformation but researchers have shown it is still widely present on the platforms.

"We believe in free expression, we believe in free debate and conversation to find the truth," Dorsey said.

Pichai, whose company owns YouTube, said after the January 6 uprising, it "removed livestreams and videos that violated our incitement to violence policies." Google's mission is "providing trustworthy content and opportunities for free expression, while combating misinformation. It's a big challenge," the CEO said.

At the same time, the Facebook founder said, "We also don't want misinformation to spread that undermines confidence in vaccines, stops people from voting, or causes other harms." He also said that the rioters and former President Donald Trump should be held accountable.

Trump was banned by Twitter over inciting violence around January 6, while Facebook has asked its independent oversight board to rule on whether to bar him permanently. He is still suspended from YouTube.

(With input from agencies)