Protesters reportedly burned the US flag and a Bible during demonstrations in Portland, Oregon, over the weekend. 

A video was posted to Twitter by user @Shelldrayk claiming to show a Bible and American flag being set alight in front of the federal courthouse in Portland.

The demonstration on Friday night was largely peaceful until the flag and Bible-burning incident, which is alleged to have taken place just after midnight, the New York Post reports.

The video, which went viral, was re-tweeted by Ian Miles Cheong, editor of the conservative political website, Human Events, who said: "I don't know what burning the Bible has to do with protesting against police brutality.

"Do not be under the illusion that these protests and riots are anything but an attempt to dismantle all of Western Civilization and upend centuries of tradition and freedom of religion." 

CBS News affiliate KOIN 6 reports that the fire was put out by members of the Moms United for Black Lives Matter group. 

Anti-racism protests have been taking place across the US since the death of George Floyd in May. 

The protests have at times been violent, with authorities in Seattle and Portland last week declaring riots. 

Donald Trump Jr commented on the Portland incident on Twitter. 

"Now we move to the book burning phase," he tweeted Saturday.

"I'm pretty sure ANTIFA doesn't actually stand for what they say it stands for. Maybe just remove the anti part of [their] name and it's perfect."