Jeremy Corbyn launched Labour's local election campaign with a scathing attack on Government-led policing cuts as he sought to shake off an anti-Semitism row ahead of polling day.
The Labour leader said leaked Home Office documents linking rising crime with shrinking police numbers exposed Amber Rudd's claims the two issues were unrelated as "absolute nonsense".
He teamed up with London Mayor Sadiq Khan at an event in central London as the capital struggles to quell surging levels of knife violence.
Labour hopes to make gains at the expense of the Tories in London, where there are elections in all 32 London borough councils.
The Labour leader also used the occasion to reaffirmed his commitment to rooting out anti-Semitism in the party after a recent string of controversies threatened to overshadow the election campaign.
On the issue of knife crime, he said: "As political leaders we must act. We have to tackle full on the reasons so many of our young people are having their lives extinguished."
Since 2010, he continued, the Conservatives have "decimated local services, the core services that are an essential part of holding our communities together".
"You simply cannot maintain community cohesion when you slash funding to the police service and cut the number of officers on our streets by 21,000.
"You cannot protect local communities when you cut funding to local councils to such an extent they are unable to provide the essential youth service support that stops many young people from being drawn into violent crime.
"The Tory record on policing and crime is one of reckless failure.
"Plain and simple - you can't have security on the cheap and cuts have consequences. Too many communities are living with those consequences."
Mr Corbyn also described attending the funerals of knife and gun crime victims, saying the experience was "deeply moving and poignant".
His speech came as the party was beset by criticism over its handling of anti-Semitism within its ranks.
Several recent revelations involving party members, including Mr Corbyn's own apparent support of a mural with anti-Semitic undertones, have led to protests against his leadership.
Mr Corbyn said: "I know my party, the party I have been a member of for 50 years and I know that the overwhelming majority of members are united, determined to root out any anti-Semitism, and to make our party the welcoming movement that it has always been.
"Prejudice and hatred of Jewish people has no place whatsoever in society and every one of us has a responsibility to ensure it is never allowed to fester again."
The Grenfell Tower disaster, which claimed 71 lives, resulted in Londoners coming together in "sorrow and solidarity" for people who had been "let down by their council and by the Government", he said.
Signalling Labour's targets on May 3, including the west London council where the fire took place, he continued: "You can have a Tory-run Barnet that has privatised almost every local service and in the process made those services worse and its workers worse off.
"Or you can have a Labour council that will bring services in-house, be accountable for their quality, invest in the delivery and treat their staff fairly and decently.
"You can have Tory-run Kensington and Chelsea whose performance was described by the Government as totally unacceptable or a Labour council that will run rogue landlords out of town and invest in building new council and social housing."
Mr Khan echoed the Labour leader's criticisms about police cuts, invoking the memory of the London riots in 2011 as evidence the Tories had not learnt lessons.
The destruction, he said, was linked to "complex root causes" such as inequality.
"The Government and the previous mayor failed to learn the lessons," he said.