Rishi Sunak has said he will hold the Met Police chief "accountable" over a pro-Palestinian march set to take place this Saturday, on Armistice Day.
The prime minister has criticised the timing of the demonstration in London as "provocative and disrespectful".
Sir Mark Rowley rejected calls by campaigners to ban the protest, saying such a move would be a "last resort".
Organisers insist their march will not go near commemorations and accuse the government of manufacturing a row.
Protests have been held in London, and other cities globally, each Saturday since the Israel-Gaza war began.
Earlier, Mr Sunak met the Met Police commissioner to seek "reassurances" that remembrance services would be safeguarded, saying there was a risk of "those who seek to divide society using this weekend as a platform to do so".
In a statement, he said police had confirmed the demonstration would be far from the Cenotaph - the focal point of remembrance services - but that Sir Mark would keep the matter under constant review based on latest intelligence.
Mr Sunak spoke of the immense sacrifices made for our freedom and peace today.
"Part of that freedom is the right to peacefully protest," he said. "And the test of that freedom is whether our commitment to it can survive the discomfort and frustration of those who seek to use it, even if we disagree with them."
The organisers of the protest have resisted police pressure to postpone the demonstrations, and accuse the government of trying to undermine their cause.
Ben Jamal, of the Palestinian Solidarity Campaign which is behind the march, said he believed the government was manufacturing a row and using the Armistice Day angle to try to "delegitimise" them.
"There's something particularly askew with an argument that says a protest calling for a ceasefire is somehow inappropriate on Armistice Day," he told the BBC.
Home Secretary Suella Braverman has accused the police of being more lax on left-wing protests than those organised by nationalists or right-wing activists.
Writing in the Times, she said there was "a perception that senior police officers play favourites when it comes to protesters".
Ms Braverman suggested there was a disparity in the policing of "lockdown objectors" and Black Lives Matter demonstrations, and said football fans were treated more harshly by the police than "politically-connected minority groups who are favoured by the left".
The home secretary has voiced her opposition to pro-Palestinian protests in the past, calling them "hate marches" in an interview with Sky News.
Protest organiser Chris Nineham, from the Stop the War Coalition, said: "We do everything we can as stewards to make sure there is nothing antisemitic or calling for violence in our demonstrations. For us, this isn't about religion, it isn't about race."
Dr Tom Thorpe, of the Western Front Association which organises the annual commemorations at the Cenotaph, said: "We don't want to stop other people enjoying their democratic rights - and we don't want them to interfere with our assembly and our ceremony that we've been doing for the last 30 years."
Earlier on Tuesday, Sir Mark said the protest organisers had shown "complete willingness to stay away from the Cenotaph and Whitehall and have no intention of disrupting the nation's remembrance events".
The demonstration on 11 November is due to begin at 12:45, more than an hour after the traditional two-minute silence.
Labour leader Sir Keir Starmer has accused the prime minister of "picking a fight" with the police over the planned pro-Palestinian demonstration.
In a post on X, Sir Keir said: "Remembrance events must be respected. Full stop. But the person the PM needs to hold accountable is his Home Secretary."
Labour's London Mayor Sadiq Khan said on X that the government should be supporting the Met, not making officers' jobs more difficult.
On Monday, the Met publicly urged organisers of the march to postpone the event, saying it would not be "appropriate".
Mr Sunak and Home Secretary Suella Braverman also criticised the timing of the event, which tens of thousands of people are expected to attend, while Conservative MP Tobias Ellwood, the former defence minister, appealed to organisers to "think again" and hold the rally on another day.
On Tuesday, Sir Mark resisted calls, including from pressure group Campaign Against Antisemitism, to request powers from the home secretary to ban the march.
The group claimed previous marches met the threshold test for public disorder that would justify the ban.
"As we approach remembrance weekend, where we remember the heroes who defended our freedoms and fought against antisemitic hatred, we must honour their memory by banning demonstrations that abuse those freedoms to call for violence against Jews," the group said.
Sir Mark said that while police can request such powers if a threat of serious disorder emerges, the "very high" threshold for doing so had not yet been reached.
He added that the use of the power was "incredibly rare" and there must be no other way for police to manage the event.
Sir Mark said he was concerned about the escalating risk of disorder caused by splinter groups breaking off from the main demonstration on Saturday, saying the threat posed by them would be monitored this week.
A former Metropolitan Police Commissioner is now urging for discussions around police operations for protests to be held privately, rather than aired publicly.
Independent crossbench peer Lord Hogan-Howe, who led the Met from 2011 to 2017, said: "We all know that there is a real challenge, both for politicians and the police, in deciding whether to ban a march. Never easy, very rarely done.
"These are difficult decisions where you are trying to balance the right to protest against the problem of serious disorder. I do worry that the pressures that are being placed on the police at the moment don't always form wise judgments in the end."
Earlier, Veterans Minister Johnny Mercer said he fully recognised "the tensions at play" but urged people to come to London for remembrance events.
"I know that elderly veterans will be coming to London and measures will all be in place to make sure that people can go about remembrance in the way they want to unmolested by any of the other events taking place this weekend," Mr Mercer said.