Sir Keir Starmer said attempts by Iran to destabilise British society “will not be tolerated” amid suspicion Tehran could be stirring up antisemitism.
The prime minister said the government was investigating whether foreign states could be behind recent attacks on the Jewish community in the UK.
Speaking to leaders of community groups, senior government ministers and police chiefs following a knife attack in Golders Green last week, Sir Keir warned there would be “consequences” if Iran was found to be responsible.
“One of the lines of inquiry is whether a foreign state has been behind some of these incidents,” he said.
“We are investigating, of course, all the possibilities. And we are clear that these actions will have consequences if that proves to be the case.
“Our message to Iran, or to any other country that might seek to foment violence, hatred or division in society, is that it will not be tolerated.”
Describing the situation as a “crisis” in the wake of the attack in northwest London last week, Sir Keir said new legislation would be rushed through to tackle “malign threats”.
The government has promised a new law to allow it to take action against state-backed groups amid calls for the proscription of Iran’s Islamic Revolutionary Guard Corps (IRGC).
Sir Keir told the meeting that although essential, security is “not enough”, as he vowed to “deal with the forces that drive this hatred in the first place”.
“We’re clear-eyed about the fact that antisemitism does not have one source alone: Islamists, far left, far right extremism, all target Jewish communities,” he said.
“That is why this government has put in place the first coordinated national plan to strengthen cohesion and confront extremism in all of its forms.”
Jewish communities across England are set to receive an extra £1m in government funding to pay for community safety work and projects aimed at countering antisemitism.
The funding follows the £25m announced last week to provide more security for the community following the attack in Golders Green.
Two Jewish men, Shloime Rand, 34, and Norman Shine, 76, were stabbed during a knife rampage on Wednesday 29 April.
Alleged attacker Essa Suleiman, 45, appeared at Westminster Magistrates’ Court on Friday and was remanded in custody.
The attack, which has been declared a terror incident by police, is the latest in a string of violent actions against Jewish people.
The locations of the incidents are close to where four Jewish community ambulances were destroyed by fire in late March.
Separately on Tuesday, counterterror police are investigating an arson attack at a former synagogue in Tower Hamlets, east London.
Jewish security charity Shomrim said fire crews were called out to the building in Nelson Street, Whitechapel, east London, in the early hours. Minor damage was caused to a set of gates and a lock at the front of the building, the Met Police said. There were no reports of injuries.
At a meeting with senior figures from the police, representatives from the arts, higher education, trade unions and businesses on Tuesday, Sir Keir said the government has ordered an independent audit of how allegations of antisemitism are handled.
“This will be a hard-edge review of where systems are failing,” he said. “We will not, and cannot, accept complacency, delays or weak enforcement, and where inconsistency is found, it will be challenged and addressed swiftly.”
He also promised new action to implement a “zero tolerance” approach to antisemitism on university campuses and action in the arts.
Universities will now be expected to “demonstrate action” to tackle antisemitism among students, while the Arts Council will be expected to withdraw funding and claw it back from anyone who is found to promote antisemitism.
