Rishi Sunak issued a damning statement against the “violent, wholly unacceptable” far-right and “Hamas sympathisers” as more than 100 were arrested on a day of protests in the capital.
More than 90 of the 126 taken in by police were counter-protesters, the majority of whom were cuffed when they tried to reach the main march.
Others were arrested after Metropolitan Police officers intercepted a “breakaway” pro-Palestine group of 150 with some of them wearing face coverings and firing fireworks at Grosvenor Place on Saturday evening.
Several of the fireworks struck officers in the face.
The Prime Minister posted on X, formally known as Twitter: “I condemn the violent, wholly unacceptable scenes we have seen today from the EDL (English Defence League) and associated groups and Hamas sympathisers attending the National March for Palestine.
“The despicable actions of a minority of people undermine those who have chosen to express their views peacefully.”
He said their actions do “not defend the honour of our Armed Forces, but utterly disrespects them”.
“That is true for EDL thugs attacking police officers and trespassing on the Cenotaph, and it is true for those singing antisemitic chants and brandishing pro-Hamas signs and clothing on today’s protest," he added.
Similarly, The Met’s Assistant Commissioner Matt Twist criticised the “extreme violence from the right-wing protesters towards the police”, calling it “extraordinary and deeply concerning”.
He said in a statement: “They arrived early, stating they were there to protect monuments, but some were already intoxicated, aggressive and clearly looking for confrontation.
“Abuse was directed at officers protecting the Cenotaph, including chants of 'you’re not English any more'.
“This group were largely football hooligans from across the UK and spent most of the day attacking or threatening officers who were seeking to prevent them being able to confront the main march.
“Many in these groups were stopped and searched and weapons including a knife, a baton and knuckleduster were found as well as class A drugs.”
While Mr Twist stressed “the Palestine Solidarity Campaign (PSC) march did not see the sort of physical violence carried out by the right-wing”, he added that “the impact of hate crime and in particular anti-Semitic offences is just as significant”.
The Met said on social media that it is looking into several accusations, including some pro-Palestine protesters allegedly wearing Hamas-style headbands and others chanting anti-Semitic slogans.
“We will soon publish images of some of those we suspect have committed these offences,” Mr Twist said.
Nine officers were injured throughout the day, with two requiring hospital treatment - one fractured an elbow and another suffered a dislocated hip.
More than 300,000 are estimated to have descended on the capital on Armistice Day, calling for a ceasefire in Gaza.
Hundreds gathered at the Cenotaph for a two-minute silence to commemorate the UK’s war dead at 11am and police said this was “marked respectfully and without incident”.
Home Secretary Suella Braverman has been accused of stoking tensions ahead of Saturday’s demonstrations, after she branded pro-Palestinian demonstrators "hate marchers" and accused the police of bias for letting the rally go ahead.
Mr Sunak is now facing calls to sack the minister, with Labour leader Sir Keir Starmer saying: "Few people in public life have done more recently to whip up division, set the British people against one another and sow the seeds of hatred and distrust than Suella Braverman. In doing so, she demeans her office."
The PM has so far maintained confidence in his Home Secretary.