Police at a vigil in memory of Sarah Everard were "placed in a position where enforcement was necessary", Scotland Yard said amid pressure to explain its handling of the event.
A crowd gathered at Clapham Common to remember the 33-year-old marketing executive, but scuffles broke out as police surrounded a bandstand covered in flowers left in tribute.
Officers from the Metropolitan Police were seen grabbing several women, leading them away in handcuffs, and the force later said four people were arrested for public order and coronavirus regulation breaches.
However, there has been condemnation of the policing of the vigil, with UK home secretary Priti Patel seeking a full report on events.
She described footage from the vigil as "upsetting", while Liberal Democrat leader Sir Ed Davey called on UK police commissioner Cressida Dick to "consider" her leadership of the force.
The mayor of London, Sadiq Khan, said the scenes were "unacceptable", tweeting: "The police have a responsibility to enforce Covid laws but from images I've seen it's clear the response was at times neither appropriate nor proportionate."
Early on Sunday assistant police commissioner Helen Ball said police were put into a position "where enforcement action was necessary".
She said: “Hundreds of people were packed tightly together, posing a very real risk of easily transmitting Covid-19.
“Police must act for people’s safety, this is the only responsible thing to do. The pandemic is not over and gatherings of people from right across London and beyond are still not safe.
“Those who gathered were spoken to by officers on a number of occasions and over an extended period of time. We repeatedly encouraged those who were there to comply with the law and leave. Regrettably, a small minority of people began chanting at officers, pushing and throwing items.”
The assembled crowd chanted “shame on you” as police led people away at the vigil, while during another confrontation a distressed woman could be heard telling officers “you’re supposed to protect us”.
Reclaim These Streets said the group was “deeply saddened and angered” by scenes of officers “physically manhandling women at a vigil against male violence”.
The group added: “This week of all weeks the police should have understood that women would need a place to mourn, reflect and show solidarity.
“Now is the time for the police and the government to recognise that the criminal justice system is failing women.
“Tonight it has failed women again in the most destructive way. We will keep fighting for women’s voices to be heard and to matter.”
Hundreds of people converged on the south London park despite an official vigil being called off earlier in the day due to police warnings over coronavirus restrictions.
Vigils also took place in locations including Glasgow, Nottingham, Birmingham and Bristol.
Separately, Sisters Uncut, an organisation describing itself as a feminist group taking direct action for domestic and sexual violence services, said it would be holding a rally at New Scotland Yard on Sunday.
Earlier on Saturday UK prime minister Boris Johnson said he and his partner Carrie Symonds would light a candle in memory of Ms Everard.
“I will do everything I can to make sure the streets are safe and ensure women and girls do not face harassment or abuse,” he said.
Appearing at London's Westminster Magistrates' Court on Saturday morning, 48-year-old police officer Wayne Couzens, spoke only to confirm his identity.
His lawyer did not enter a plea to the charges of kidnap and murder ahead of a fuller court hearing scheduled for Tuesday. He remains in custody.
Police discovered Ms Everard’s body on Wednesday in woodland about 80km southeast of London. The court heard that her body was found in a builder’s refuse bag, and was identified using dental records.
Couzens joined the Metropolitan Police in 2018 and guarded foreign embassies before his arrest.
England’s police watchdog has launched an investigation into the Metropolitan Police’s handling of the case.