The number of national security cases involving hostile states carrying out operations such as spying and sabotage in the UK has increased by half in six months, the head of counter-terrorism policing has said.

As the security services continue to investigate the potential involvement of an Iran-linked group in Monday’s attack on community ambulances run by a Jewish charity, the assistant Metropolitan police commissioner Laurence Taylor warned of a worrying trend.

“We’ve seen a very significant increase in our work involved with foreign state activity, particularly around that top three of Iran, Russia and China,” he said. “In the six months up to December last year, we had a 50% increase in national security act investigations, and that’s on the back of a five-fold increase over the last four or five years. It is a significant part of our case load.”

A group called Harakat Ashab al-Yamin al-Islamia, whose name translates as the Islamic Movement of the Companions of the Righteous, has claimed responsibility for the firebombing of four ambulances in Golders Green, north London.

The ambulances belonged to the Jewish charity Hatzola and had been parked near the Machzike Hadath synagogue.

The claim of responsibility is yet to be verified and the incident is being treated as an antisemitic rather than a terrorist attack.

The Met has said it will deploy an extra 264 officers as well as specialist teams including firearms and drones to boost security for Jewish communities in the run-up to Passover in early April.

At a time of heightened tension, the Conservative leader, Kemi Badenoch, suggested tougher immigration rules would help to tackle antisemitism, saying that people were entering the UK from “cultures where there is a history of hatred against Jews”.

She made her comments during a visit on Tuesday to a Jewish volunteer ambulance service in Stamford Hill, north London.

“I think the government needs to move beyond words to action,” she said. We are seeing an increase in attacks on the Jewish people, the Jewish community, Jewish businesses, and it is not enough just to offer to step up security.

“That’s barely the first step. What I want to see is sanctions against people who are inciting violence against Jewish people, inciting hatred against Jewish people.

“In the public sector in particular, where the government does have levers … you know, I’ve heard stories about medical staff refusing to treat Jewish people. They should lose their jobs.

“But we also need to do something about people coming into our country from different cultures where there is a history of hatred against Jews.

“This is one of the reasons why we have already toughened up our immigration policy, saying that we will leave the ECHR,” she said in reference to the European convention on human rights.

“We need to look at every single cause, not just the symptoms, and if we address that, then we’ll be able to deal with antisemitism.”

King Charles accepted the role of patron at a charity that protects Jewish communities on Monday evening.

The Community Security Trust (CST) said the king’s acceptance of the position highlighted his support for the “fight against antisemitism”.

The new role is understood to have been part of a regular review of royal patronages rather than being linked to Monday’s incident.

Four ambulances on loan from the government arrived to replace the destroyed vehicles on Tuesday. The prime minister has said it will meet the costs of permanent replacements.