Jeremy Corbyn has turned his fire on Theresa May's record on dealing with the terror threat, accusing her of denying resources to the police and security services and suppressing a report believed to make sensitive allegations about Saudi funding of extremists.
And he sought to end the earlier controversy over his support for police use of "shoot-to-kill" tactics against armed attackers, by stating that he backed the "full authority for the police to use whatever force is necessary to protect and save life as they did last night, as they did in Westminster in March".
In a speech in Carlisle a day after the terror attack at London Bridge, the Labour leader vowed to take "whatever action is necessary and effective" to preserve public safety. And he warned the Government it could not "protect the public on the cheap".
The Prime Minister cut police manpower by 20,000 despite warnings that this would undermine safety, said Mr Corbyn, who has promised to recruit an additional 10,000 officers and 1,000 security service agents if he wins power on June 8.
Earlier in the day, Mrs May set out a four-pronged strategy to tackle terror by countering radical ideology; clamping down on online extremism; preventing the growth of segregated communities; and giving extra powers to police, security agencies and courts.
The PM's comments sparked complaints from Labour that she was getting involved in political debate on a day when the parties had agreed to halt election campaiging until the evening.
Mr Corbyn backed Mrs May's insistence that the General Election must go ahead on June 8.
He said the attacks at Manchester Arena and London Bridge had turned Thursday's vote into a "struggle between terrorism and democracy itself".
He urged voters to "resist Islamophobia and division and turn out on June 8 united in our determination to show our democracy is strong".
Speaking as the brief pause in campaigning came to an end, Mr Corbyn said: "Our priority must be public safety and I will take whatever action is necessary and effective to protect the security of our people and our country.
"That includes full authority for the police to use whatever force is necessary to protect and save life as they did last night, as they did in Westminster in March."
Criticising Mrs May's record, he said: "You cannot protect the public on the cheap. The police and security services must get the resources they need, not 20,000 police cuts.
"Theresa May was warned by the Police Federation but she accused them of 'crying wolf'.
"We will recruit another 10,000 new police officers, including more armed police, as well as 1,000 more security services staff to support our communities and help keep us safe."
After Mrs May said that combating terrorism would require "difficult conversations" with Muslim communities in the UK, Mr Corbyn said that the PM must also be ready to have difficult discussions with close ally and major arms customer Saudi Arabia about terror funding.
He cited the delayed publication of an investigation commissioned by David Cameron into the foreign funding of extremist Islamist groups, which is reported to focus on the Gulf kingdom.
"We do need to have some difficult conversations, starting with Saudi Arabia and other Gulf states that have funded and fuelled extremist ideology," said Mr Corbyn.
"It is no good Theresa May suppressing a report into the foreign funding of extremist groups. We have to get serious about cutting off the funding to these terror networks, including Isis, here and in the Middle East."
Mr Corbyn said that the terrorists' aim was "plainly to derail our democracy and disrupt or even halt this election".
"The mass murderers who brought terror to our streets in London and Manchester want our election to be halted," he said.
"They want democracy halted. They want their violence to overwhelm our right to vote in a fair and peaceful election and to go about our lives freely.
"That is why it would be completely wrong to postpone next Thursday's vote, or to suspend our campaigning any longer."
Mr Corbyn took a swipe at Donald Trump over the president's attack on London Mayor Sadiq Khan for supposed "political correctness" over the terror attack.
Mr Trump criticised the mayor for saying Londoners should not be "alarmed".
But Mr Khan accused him of deliberately misinterpreting comments in which he urged Londoners and visitors not to be alarmed by the sight of armed police on the streets.
The Labour leader said: 'At this time it is more important than ever that we stay united in our communities. It is the strength of our communities that gets us through these awful times as London Mayor Sadiq Khan recognised but which the current occupant in the White House has neither the grace nor the sense to grasp.
"Whether we are Muslim or Christian, black or white, male or female, gay or straight, we are united by our values, by our determination for a better world, and that we can build a better society."
Mr Corbyn - who called a minute's silence before beginning his speech - said that if elected on Thursday, he will commission a report on the terror threat on his first day in Downing Street
"We are ready to consider whatever proposals may be brought forward by the police and security services more effectively to deal with the terrorist threat," said the Labour leader.
"If Labour is elected I will commission a report from the security services on Friday on the changing nature of the terrorist threat."
He also said that on his first day in office he would ask the Commissioners of the Metropolitan Police and the British Transport Police for the names of those whose bravery had been on show at the terror attacks, so that he can "acknowledge their heroism and of many others in our emergency services and among the public who intervened".
Returning to his regular campaign theme, Mr Corbyn said he did not hesitate to make the case for "more tax from those who can afford it" to pay for services like the police.
"It is taxation that underpins our peaceful, tolerant and civilised society - the police, security services, fire and rescue service, our NHS," he said. "They have all suffered cuts to pay for tax giveaways for the big corporations and the very richest."
After the speech, Mr Corbyn invited about 100 supporters who had gathered in the car park of the County Hotel in Carlisle inside for a private meeting.
For Conservatives, security minister Ben Wallace said: "This was a hastily-arranged speech designed to help Jeremy Corbyn run from his record on counter-terrorism policy, but it failed.
"He has boasted about opposing every single counter-terror law, opposed the use of shoot-to-kill, and gave cover to the IRA when they bombed and shot our citizens.
"Voters will judge him on his views and actions in the last 30 years, not his desperate promises and evasive soundbites three days out from polling day.
"There's a clear choice at this election: Theresa May managing Brexit and delivering security for ordinary working families, or Jeremy Corbyn negotiating Brexit, Diane Abbott in charge of our national security, and John McDonnell in charge of our economy."
Loud cheers could be heard from the private meeting, which was closed to the media.