US President Donald Trump is under fire for refusing to denounce white supremacy and his comments about a far-right extremist group.
During the first presidential debate on Wednesday, host Chris Wallace asked Trump if he was "willing to condemn white supremacists and militia groups" in the US over their involvement in protests against police brutality, which often turned to violence.
"Sure. I'm willing to do that," Trump said, before faltering.
He instead asked Wallace again on what kind of groups he was meaning. Wallace suggested the Proud Boys, a far-right extremist group.
But instead of condemning them, Trump said: "Proud Boys - stand back and stand by".
He then blamed the violence on the left-wing.
"I'll tell you what - I'll tell you what - someone has to do something about Antifa and the left. This is not a right-wing problem. This is left-wing."
On Wednesday night the Proud Boys said on social media they took Trump's comments as a call to action and an endorsement of their cause.
But on Thursday, Trump shifted course claiming that he does not know who the Proud Boys are, the Independent reported.
So who are the Proud Boys and Antifa?
The Proud Boys
The Proud Boys are a neo-fascist, far-right group founded by Canadian - British far-right activist and the co-founder of Vice magazine Gavin McInnes.
McInnes founded the group in 2016 in the lead up to Trump becoming President and it is mostly based in the western United States.
But the group is believed to be very small, with only a few hundred members in the United States, the Guardian reported.
They also have a presence in other countries including Canada, the United Kingdom and Australia.
The Southern Poverty Centre lists it as a hate group and said they are "known for anti-Muslim and misogynistic rhetoric".
However, the group has denied bigotry and said they just aim to stick to "western" values.
They are generally pro-gun rights, against feminism and gender quality and take a libertarian stance.
The Proud Boys also only admit men, who endure a violent "hazing" process and members must declare they are "a Western chauvinist who refuses to apologise for creating the modern world".
Antifa is a shortened version of "anti-fascism" and is considered an idea, not an organisation.
The Anti-Defamation League (ADL) described them as "a loose collection of groups, networks and individuals who believe in active, aggressive opposition to far right-wing movements".
The Southern Poverty Centre said: "the Trump administration frequently uses the term [Antifa] to describe any group or individual that demonstrates in opposition to its policies".
The movement began in the 1960s in Europe and their ideology is rooted in the assumption that the Nazi party would not have been able to come into power if people had more aggressively fought them in the streets, the ADL said.
In August 2017, the group gained new prominence in the United States after the Unite the Right rally, a white supremacist and neo-Nazi rally that took place in Charlottesville, Virginia.
Most Antifa come from the far-left and they confront what they believe to be authoritarian movements and groups.
In August, a self-described anti-fascist, Michael Reinoehl, fatally shot a supporter of Patriot Prayer, a Portland-area group that is known to march with the Proud Boys. Reinoehl was shot dead by police the following week, BBC reported.
No one knows how many members of the movement there are.
Correction: An earlier version of this article stated that there are no deaths linked to Antifa groups. This has been updated.