Far-right protesters have fought with police after hundreds of people gathered to “guard” statues in central London.
Footage showed demonstrators throwing bottles at riot officers in Whitehall on Saturday.
In another clash near Parliament Square protesters also appeared to hurl smoke bombs.
The crowd claimed to be in the capital to protect monuments including former prime minister Winston Churchill’s statue, which was vandalised last week during an anti-racism demonstration.
The protest on Saturday was attended by the leader of the far-right group Britain First Paul Golding.
He said: “Anyone who comes along today to try and vandalise them (monuments) will probably be dealt with by all of these Englishmen that turned up, and they’re fed up as well.”
LBC reporter Matthew Thompson claimed the demonstrators had turned on journalists as well.
He tweeted: “And you can see as a protestor smacks my phone out of my hand as I try to film the scuffles.”
There were also claims some of the protesters performed a Nazi salute near the Churchill statue (in the video above).
Former Lord Mayor of Sheffield Magid Magid added on Twitter: “While doing the nazi salute to the Churchill statue!?”
Black Lives Matter had originally been planning a demonstration but decided to cancel the event on Friday to avoid clashes with far-right groups.
The Churchill statue and a memorial to slave trader Edward Colston were vandalised during anti-racism protests last weekend, which prompted far-right groups to organise their own counter-demonstration.
Police have told those planning on joining demonstrations on Saturday they must be off the streets by 5pm.
In an attempt to avoid a repeat of last week’s violent clashes with police, anti-racism protesters have been told they must stick to the planned route that will run from Hyde Park to Whitehall.
The force fear the protests – that were sparked by the death of George Floyd in the US last month – could be hijacked by counter-demonstrations by far-right groups.
Met Police have issued a Section-60 order for the protests in the capital, which increases their stop and search powers.
A spokesman for Scotland Yard said: “We have learnt that some people are coming into London to cause harm and are likely to bring weapons with them.”
Protesters also flocked to George Square in Glasgow to “protect” a war memorial.
In an event organised by a group called the Loyalist Defence League (LDL), people congregated to stop vandalism to the Glasgow Cenotaph, erected to commemorate the lives of those who died in the First World War.
The group was penned in on the east side of the square, with a similar-sized area reserved for counter-protesters which remained empty.
Several hundred people have gathered outside City Hall in Belfast to apparently do the same.
The Northern Ireland Cenotaph Protection Group (NICPG) issued a statement saying its aim is to protect war memorials amid attacks on statues of historical figures across the UK in recent days.
The London mayor earlier defended his decision to board up the Churchill monument ahead of the marches.
Khan said the decision to protect the statue in Parliament Square – along with the Cenotaph and monuments to Nelson Mandela and Mahatma Gandhi – was a “wise” precaution.
Following the toppling last weekend of the statue of Colston in Bristol, he said there were fears the London statues could become a “flashpoint for violence” involving extreme far-right protesters.