Jeremy Corbyn will draw links between Britain's involvement in military interventions overseas and terrorism at home, as he resumes Labour's General Election campaign four days after the Manchester bomb attack.
In a speech in London on Friday, the Labour leader will make a veiled criticism of Conservative-led administrations, stating it is the "responsibility" of governments to minimise the risk of terror by giving police the funding they need and ensuring their foreign policy does not heighten the threat to the UK.
Mr Corbyn will promise a Labour government will provide the funding that security agencies and emergency services need, and will adopt a new approach towards countries which act as a seedbed for extremist violence, declaring it is time to recognise the West's "war on terror" is not working.
All the major parties are expected to resume national campaigning for the June 8 election on Friday, though Prime Minister Theresa May will not be involved as she is in Italy for a summit of the G7 group of industrialised nations.
In what is likely to be seen as a reference to Britain's military involvement in wars in Iraq and Afghanistan as well as air strikes against terrorist targets in Syria - all of which he opposed - Mr Corbyn will say Labour would "change what we do abroad" if it wins power.
"Many experts, including professionals in our intelligence and security services, have pointed to the connections between wars our government has supported or fought in other countries and terrorism here at home," Mr Corbyn will say.
"That assessment in no way reduces the guilt of those who attack our children. Those terrorists will forever be reviled and held to account for their actions.
"But an informed understanding of the causes of terrorism is an essential part of an effective response that will protect the security of our people that fights rather than fuels terrorism.
"We must be brave enough to admit the 'war on terror' is simply not working. We need a smarter way to reduce the threat from countries that nurture terrorists and generate terrorism."
Mr Corybn will say the "solidarity, humanity and compassion" shown on the streets of Manchester in the days following Monday's atrocity would be the values which guide his government in office.
And, in what may be an attempt to fend off allegations of a lack of patriotism, he will say: "There can be no love of country if there is neglect or disregard for its people."
He will say: "No government can prevent every terrorist attack. If an individual is determined enough and callous enough sometimes they will get through.
"But the responsibility of government is to minimise that chance - to ensure the police have the resources they need, that our foreign policy reduces rather than increases the threat to this country and that at home we never surrender the freedoms we have won and that terrorists are so determined to take away."
Reversing Conservative cuts to emergency services and police will form part of Labour's response to terrorism, Mr Corbyn will suggest.
"To keep you and your family safe, our approach will involve change at home and change abroad," he will say.
"At home, Labour will reverse the cuts to our emergency services and police. Once again in Manchester, they have proved to be the best of us.
"Austerity has to stop at the A&E ward and at the police station door. We cannot be protected and cared for on the cheap.
"There will be more police on the streets under a Labour Government. And if the security services need more resources to keep track of those who wish to murder and maim, then they should get them."
Former Liberal Democrat leader Lord (Paddy) Ashdown said: "Some political leaders have sought to politicise the events of the week, but now is not the time, and this is not the event, to seek political advantage.
"The families of victims in Manchester have a right to expect political parties to respond with restraint and sensitivity to these unpardonable crimes.
"There will be a moment when we will want to look at the policy implications of what has happened, but that should not be in the shadow of these terrible events when the nation should stand together."
Labour's former home secretary Charles Clarke told BBC2's Newsnight: "I've not taken Jeremy's advice on security matters for some decades now, and I don't with his remarks tomorrow."
Mr Clarke, who was home secretary at the time of the July 7 attacks in London in 2005, said: "The core attacks from 9/11 and beforehand have come from forces which are about trying to destroy the whole of our society - this is before the Iraq war, before the wars in Syria.
"The motive force is about the destruction of all the core elements of our society. That's not something which is about a foreign policy conflict - something in Syria, something in Iraq, whatever it might be. It's about a totally opposed vision of what society should be.
"I've never thought he's prime ministerial material. I didn't support him for leader of the Labour Party."