It follows last week's violence in Washington when supporters of President Donald Trump stormed the US Capitol.

"Given the violent events in Washington, DC, and increased risk of harm, we began permanently suspending thousands of accounts that were primarily dedicated to sharing QAnon content on Friday afternoon", Twitter said in a blog late on Monday.

"These accounts were engaged in sharing harmful QAnon-associated content at scale and were primarily dedicated to the propagation of this conspiracy theory across the service", the company said.

QAnon backers have pushed conspiracies on social media that include the baseless claim that Trump secretly is fighting a cabal of child-sex predators, among them prominent Democrats, figures in Hollywood and "deep state" allies.

The social media company also said it would be limiting engagement on some tweets by not allowing them to be shared or replied to, as it had previously done with the president’s posts, as well as blocking certain keywords in its search function that violates the company’s policies.

Twitter had said on Friday it would permanently suspend accounts pushing QAnon content, banning prominent right-wing boosters of its conspiracy theories.

The company said it would “permanently suspend accounts Tweeting about these topics that we know are engaged in violations of our multi-account policy, coordinating abuse around individual victims, or are attempting to evade a previous suspension.”

“With continued attempts to organise events against the outcome of the US presidential election that can lead to violence, and use of the term by those involved in Wednesday’s violence in DC, we’re taking this additional step in the lead up to the inauguration”, the company said in a statement.

The storming of the Capitol building last week by Trump supporters delayed the certification of Biden's election victory.

Lawmakers were forced to flee, as the building was mobbed by the president's supporters who overwhelmed security forces. Five people died in the violence including one Capitol Police officer who was beaten as he tried to ward off the crowds.

Additional reporting by agencies