After the latest attack, at Kenton United Synagogue in the Harrow area of the city shortly after midnight - the third such incident in a week - United Kingdom counter-terrorism police said they were heading up investigations into the incidents.
A pro-Iranian government group, which says it is also behind a spate of attacks across Europe on United States, Israeli and Jewish targets, has said it was responsible.
"As the conflict in the Middle East continues to evolve, counter-terrorism policing and our partners remain alive to the threat of Iranian hostile activity in the UK," Vicki Evans, senior national co-ordinator for Counter Terrorism Policing, told reporters.
"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."
Chief Rabbi Ephraim Mirvis said the Kenton fire, which did not cause any significant damage, was the third "cowardly" attack on Jewish sites in the UK capital in less than a week.
"A sustained campaign of violence and intimidation against the Jewish community of the UK is gathering momentum," Mirvis said on X.
"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 Friday night, there was an attempted arson attack on a business premises with links to the Jewish community while a few days earlier police arrested two suspects over an attempted arson attack on another synagogue in the capital.
Meanwhile an area around the Israeli embassy in London was cordoned off following an online report that it had been targeted with drones carrying "dangerous substances".
Police later said items they found did not contain any harmful or hazardous substances.
Last month, several ambulances belonging to the Jewish volunteer emergency service Hatzola, which were parked near a synagogue in Golders Green, were torched.
Police said they had boosted their presence in the area, and it was officers on a "deterrence" patrol shortly after midnight who spotted a window at the Kenton synagogue had been damaged.
They found an accelerant had been thrown inside.
UK Prime Minister Keir Starmer said he was appalled by the attempted anti-Semitic arson attacks.
"This is abhorrent and it will not be tolerated. Attacks on our Jewish community are attacks on Britain," he wrote on X.
The Pro-Iranian group Harakat Ashab al-Yamin al-Islamia, (HAYI) or Movement of the Companions of the Right Hand of Islam, has said it is responsible, and posted a video purporting to show the attack on the Kenton synagogue on social media.
"This same group has claimed several incidents over recent months at places of worship, business and financial institutions across Europe," Evans said.
"These locations all appear to be linked to Jewish or Israeli interests."
