Three people have been charged after four ambulances run by the Jewish volunteer service Hatzola were deliberately burned in a synagogue car park in Golders Green in the early hours of 23 March.
Two men, aged 20 and 19, and a 17-year-old with dual British-Pakistani nationality face counts of arson and of acting in a way that could have endangered life.
All three were arrested on Wednesday at separate addresses in east London and are due to appear at Westminster Magistrates' Court on Saturday.
The Metropolitan Police say counter-terrorism officers are leading the inquiry, although the incident has not been formally classified as terrorism.
Earlier in the investigation two other men, aged 45 and 47, were detained and later released on bail until late April.
Frank Ferguson, who heads the Crown Prosecution Service's special crime and counter-terrorism unit, reminded the public that legal proceedings are ongoing and that the defendants are entitled to a fair trial.
Police commanders said officers have been working around the clock to identify those responsible and praised the local community for its support since the attack.
Hatzola — a volunteer ambulance group serving people of all faiths — said its vehicles were targeted while parked at the synagogue.
Patrols have been stepped up in neighbourhoods with large Jewish populations as a precaution, particularly during the Passover period, senior officers added.
They stressed the extra presence is intended to reassure residents and is not a response to any specific new threat.
