Facebook has announced a ban on all accounts linked to the far-right QAnon conspiracy group, as the social network tries to clamp down on misinformation ahead of the US presidential election.

Facebook staff will now seek out and delete QAnon groups and pages on both Facebook and Instagram, the company said in a blog post.

The QAnon movement grew from an anonymous 2017 posting claiming bizarre child exploitation and political plots, and has earned a place in President Donald Trump's Twitter stream.

He has praised the group as patriotic, and more than a dozen Republican congressional candidates have promoted it.

Researchers say recent QAnon posts have spread false information about voting and about Covid-19, even claiming that Mr Trump faked his Covid-19 diagnosis in order to orchestrate secret arrests.

The FBI last year said in a report that QAnon was one of several movements that could drive "both groups and individual extremists to carry out criminal or violent acts".

QAnon's core claim is that President Trump is secretly leading a crackdown against an enormous paedophile child sex-trafficking ring that includes prominent Democrats and the Hollywood elite.

No part of the theory is based on fact.