Attacks on the Jewish community are "gathering momentum", the Chief Rabbi says, after another arson attack was reported at a north-west London synagogue.
The warning comes after Kenton United Synagogue in Harrow was attacked overnight, the latest in a series of arson attacks on Jewish properties this month.
Counter-terrorism police are investigating whether they are linked to a group with possible ties to Iran, with officers warning those involved will face serious prosecution under national security laws.
Chief Rabbi Sir Ephraim Mirvis described the latest attack as "cowardly" while Prime Minister Sir Keir Starmer said he was appalled and that "visible policing" would be increased.
At a press briefing outside Kenton United Synagogue on Sunday, deputy assistant commissioner Vicki Evans said the incidents were similar in nature and had been claimed online by a group called Ashab al‑Yamin, which had also claimed attacks on Jewish targets across Europe.
"We are aware of public reporting that suggests this group may have links to Iran - as you would expect we will continue to explore that question as our investigation evolves," she said.
"I've spoken previously about the Iranian regime's use of criminal proxies, and we're considering whether this tactic is being used here in London.
"This is recruiting violence as a service, and the people who conduct that violence often have little or no allegiance to the cause and are taking quick cash for their crimes."
Evans added anyone who was identified could be prosecuted under the National Security Act, which carried "significant sentences and lifetime restrictions".
The Met said counter-terrorism officers were investigating the latest attack as well as one at Finchley Reform Synagogue, another at a building used by a Jewish charity in Hendon, and ambulances belonging to a Jewish charity set alight in Golders Green last month.
An arson attack at a Persian language media organisation is also being investigated.
At Kenton synagogue, the Met said officers on "deterrence and reassurance patrols" noticed damage to a window overnight.
"On further inspection they saw smoke inside a room and evidence that a bottle with some sort of accelerant had been thrown through the window," the force said.
"The London Fire Brigade was called and firefighters searched the building to confirm that there was no further fire risk."
No-one was injured and minor smoke damage was reported.
Yehuda Black, the synagogue's rabbi, said the item was thrown into the medical room.
"I was very upset to hear about what happened. Our synagogue is a beautiful synagogue," he said.
"It's so unfortunate that it has been damaged in such a way."
The synagogue was closed following the attack but there were hopes it would reopen in a few days.
Sir Ephraim wrote on social media: "Last night yet another synagogue, this time in Kenton, was targeted in a cowardly arson attack."
He added: "A sustained campaign of violence and intimidation against the Jewish community of the UK is gathering momentum.
"This sustained attack on our community's ability to worship and live in safety is an attack on the values that bind us all together.
"Thank God, no lives have been lost, but we cannot, and must not, wait for that to change before we understand just how dangerous this moment is for all of our society."
On social media, Sir Keir wrote: "This is abhorrent and it will not be tolerated. Attacks on our Jewish community are attacks on Britain.
"We are increasing visible policing and those responsible will be found and brought to justice. We will not rest in the pursuit of perpetrators."
Sir Sadiq Khan said "history shows that we will never back down against terrorists".
In a statement, the mayor of London added: "There can never be any justification for attacking our Jewish friends, neighbours and colleagues. Those responsible are seeking to promote fear, hatred and division.
"They can't stand what our city represents - an open, diverse, pluralistic society that embraces and celebrates our differences."
The Community Security Trust (CST), an organisation which provides security for Jewish people, said thanked the police and London Fire Brigade for responding quickly.
"We are supporting the affected location and are working closely with the police as they investigate and seek to identify those responsible," a spokesperson added.
The Campaign Against Antisemitism said this was now "terrifyingly becoming a spate of daily arson attacks on the Jewish community".
United Synagogue, an organisation that Kenton synagogue is a part of, said: "A synagogue is not just a building, it is a place of worship, community and - theoretically - safety.
"To target it in this way is a deeply disturbing act that strikes at the heart of Jewish life."
The organisation's president, Saul Taylor, added: "The prime minister should declare publicly what the Jewish community has known for some time, this is an epidemic of anti-Jewish hate."
On Saturday evening the Met Police said it was increasing patrols across north‑west London, with more officers, stop and search powers, and armed and counter‑terrorism units deployed to protect communities and deter further incidents.
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