UK foreign policy would change under a Labour government to one that “reduces rather than increases the threat” to the country, Jeremy Corbyn is to say.
As election campaigning resumes after the attack in Manchester, the Labour leader will point to links between wars abroad and “terrorism here at home”.
In a speech, Mr Corbyn will say the “war on terror is simply not working”.
Meanwhile, PM Theresa May will chair a session on counter-terrorism with G7 leaders in Sicily, Italy, on Friday.
She is expected to focus on what can be done to deal with the threat posed by extremists online.
She will urge a common approach to dealing with tech companies, which she says have a “social responsibility” to remove harmful content.
In London, Mr Corbyn will deliver his speech as the bigger political parties return to the campaign trail following Monday night’s suicide bombing at Manchester Arena that killed 22 people, many of them children, and injured 116.
According to pre-released excerpts from his speech, Mr Corbyn will pledge a “change at home and change abroad” if Labour wins power.
He will say that “many experts… have pointed to the connections between wars our government has supported or fought in other countries and terrorism here at home”.
“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.”
Mr Corbyn, who opposed UK military intervention in Iraq and Afghanistan, and voted against strikes in Libya and Syria, will say: “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.”
He will also pledge to “reverse the cuts to our emergency services and police”, arguing that “we cannot be protected and cared for on the cheap”.
‘Austerity must stop’
Paying tribute to the “solidarity, humanity and compassion” of the people of Manchester, he will say those are the values that would guide a Labour government.
He will add: “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.”
A Labour government would fund more police and ensure the security services had sufficient resources “to keep track of those who wish to murder and maim”, he will say.
“Austerity has to stop at the A&E ward and at the police station door,” he will say.
Labour’s former home secretary, Charles Clarke, told BBC Newsnight that Mr Corbyn was “simply wrong” about the war on terror.
He added: “The motive force is about the destruction of all the core elements of our society and that’s not something that’s 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.”
Former Lib Dem leader Lord 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.”
“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.”
UKIP, which resumed campaigning on Thursday by launching its manifesto, has pledged to beef up security in the wake of the arena bombing by increasing numbers of police officers, troops and border guards.
While leader Paul Nuttall said he was not blaming the prime minister personally for the attack, his deputy chairwoman Suzanne Evans said Theresa May “must bear some responsibility”.
“All politicians who voted for measures to make cuts bear some responsibility… when 9/11 happened, we should have had a serious rethink about immigration. It didn’t happen.”