London: A senior Scotland Yard officer has said radical “societal change” is needed to stem a rising tide of homicides after detectives arrested a man on suspicion of the murder of a teenage girl that brought national attention to London’s violent crime crisis.

DCS Michael Gallagher, the head of the Metropolitan police’s organised crime command and former lead on knife crime, said action was needed from government, parents and communities as Britain’s largest force could not arrest its way out of the problem.

On Saturday, however, the mayor of London again said the Met would increase the use of stop-and-search powers, placing him on a collision course with Labour colleagues and activists who say the tactic poisons relations between police and London’s black and minority communities.

Sadiq Khan told BBC Radio 4’s Today programme: “What you will see over the course of the next few weeks and months is what we have seen over the last few weeks and months, which is stop-and-search based on suspicion of carrying an offensive weapon going up, more arrests as a consequence of this intelligence-led stop-and-search going up, and hopefully our city becoming safer.”

The Met commissioner, Cressida Dick, used a BBC interview to announce that the force would deploy 300 extra officers a day to the areas of London most affected by violence. A spokeswoman for Scotland Yard said the force would not reveal which areas these were.

A sharp increase in killings in London, with more than 50 so far this year, has led to emergency talks between police and community groups.

On Friday, as Scotland Yard convened an emergency meeting with community groups to discuss the killings, police hunting those behind the shooting of 17-year-old Tanesha Melbourne-Blake arrested a suspect.

The teenager, who was killed in Tottenham on Monday, is increasingly believed to have been an innocent bystander hit outside her boyfriend’s house by a gunman who opened fire as part of a gang feud fuelled by taunts on social media.

Gallagher said more focus was needed on the needs of the young, with mostly young men being killed and doing the killing. “What we need is a societal change where young people, as perpetrators and victims, feel valued and protected,” he said. “It is beyond the police. We cannot prosecute our way out of this.

“We absolutely need to work with everyone, everybody. Parents, government, community groups.”

Gallagher has previously warned that youth violence may get worse over coming years as London’s demographics change, with the population forecast to grow to 10 million by 2030. He said: “It is difficult, but every police officer is doing their best.”

Dick said the force was not in crisis but added: “This is not an unprecedented time, but it is a very worrying time.”

She said her force had “not lost control” of the streets, in reply to a Guardian interview in which the former Met senior officer Victor Olisa said that was the view of officers and communities.

The government will launch an anti-violence strategy next week aiming to make good on a promise first made by Tony Blair to be tough on the causes of crime, as well as strong punishments for offenders.

Governnment sources say they are still not convinced that increased stop and search reduces violence, saying the evidence shows no link. Dick says she will back her officers in its use where it is justified, following calls by some for it to be increased.

When the practice was at its height in 2011-12, the Met was conducting more than 500,000 stops a year, disproportionately targeting African-Caribbean people, with the vast majority of searches producing no evidence of crime but poisoning community relations. Since April 2017, the Met has carried out 115,000 stops.

A meeting was held at the Met’s headquarters on Friday morning with community groups. One source said people left more angry than when they arrived and had no idea what the force was planning to do.

The source said: “From the meeting, it doesn’t seem the Met have a grip on what’s going on. There was a lot of anger.”

Nicola Calica-Myall, an activist against knife crime whose son was stabbed 37 times aged 17 but survived, was at the meeting. “It’s important to know that our fears as a community are being recognised and things are in place,” she said. “It’s everybody’s problem and more Londoners need to recognise this situation may not go away any time soon.”

Police chiefs want to develop a “mobilisation plan” to tackle violent crime.

One senior Met source said the sustained rise in killings and violent crime had come as a surprise and the causes for the change were unclear. London recorded more killings in February and March in London than New York , which was once a byword for out of control violent crime.

Scotland Yard chiefs are, to an extent, at the mercy of events, with seven stabbings on Wednesday evening alone, adding to the urgency for a change in approach from the police and politicians.

Detectives said they had arrested a 30-year-old man for the shooting of Melbourne-Blake. DI Beverley Kofi, of the Met’s homicide and major crime command, urged people with information to come forward: “You may be fearful of repercussions of speaking to police, or have loyalties that you believe can’t be compromised. We are dealing with the fatal shooting of a teenage girl, and would implore you to do the right thing and come forward.”

Dick said the Met was confident it would bring people to justice. “In the five cases in the last week that will be on your mind, we have arrested in all but one,” she said. “I anticipate that we will have further arrests, and indeed charges.”

The shooting of Melbourne-Blake in Tottenham was followed 30 minutes later by the gunning down of 16-year-old Amaan Shakoor in Walthamstow, east London.

On Wednesday, an 18-year-old male was stabbed in Hackney and died shortly afterwards. The same day, a 53-year-old man died after a fight at an east London betting shop. His murder is being investigated with officers from outside the Met, because homicide detectives from the force are overrun.

Three teenage boys have been charged with offences in connection with the stabbing of a 13-year-old boy in east London on Thursday . A 13-year-old and two 16-year-olds were charged with wounding with intent and will appear at Thames magistrates’ court on Saturday, police said.