The Jewish holy symbol alongside the numbers "9 11" was spray-painted in red and purple on several premises in the Hampstead and Belsize Park area, including South Hampstead Synagogue.

The graffiti references an anti-Semitic conspiracy theory that Jews are responsible for the 9/11 terror attack.

Police have said they are investigating the racially motivated hate crime after receiving reports of the vandalism at 11.30pm on Saturday.

Conservative councillor for Hampstead Oliver Cooper said he spent Sunday morning patrolling the neighbourhood after "appalled" residents alerted the Community Security Trust (CST) charity, which works to protect the Jewish community.

Mr Cooper said: "My first reaction was shock and horror.

"I've had to report anti-Semitic graffiti in Hampstead a number of times before, including by a banned neo-Nazi group, but I have never seen anything approaching this extent."

He added: "I was alerted to these incidents by a number of neighbours, who had reported it to the Community Security Trust.

The graffiti references an anti-Semitic conspiracy theory that Jews are responsible for the 9/11 terror attack. Picture: PA

"I spent this morning walking around Hampstead to find all the locations so that they could be removed as quickly as possible, and to reassure residents that were naturally appalled by it that the police and CST were already aware and taking it as seriously as it deserved to be."

Mr Cooper said he came across the graffiti in nine places, and others also posted photographs of the markings on Twitter.

Jewish comedian and writer, David Baddiel described the graffiti as: "depressingly similar to what my grandparents would've seen in their neighbourhood, the one they had to flee from in 1939."

The Metropolitan Police said no arrests have yet been made.

Inspector Kev Hailes said: "This is clearly a concerning incident and one we are taking seriously.

"We have liaised with our partners in order to remove the graffiti and various inquiries are under way to find who is responsible.

"Officers will be on patrol throughout the area in order to provide some reassurance to local communities. Please approach us if you have any questions or concerns."

Police have asked anyone who saw anything suspicious on Saturday night to call them on 101.

The incident comes after five people were stabbed at a rabbi's home north of New York on Saturday night.

A knifeman attacked a Hanukkah celebration in Monsey, before fleeing in a vehicle at around 10pm, police said.

The attack appeared to be the latest in a string targeting Jews in the region, including a massacre at a kosher grocery store in New Jersey earlier this month.

Responding to the graffiti in London, the Board of Deputies of British Jews wrote on Twitter: "This is a reminder that antisemitism is still with us. Thanks @CST_UK for reporting to @MPSCamden. We hope action is taken to find & punish the perpetrators. Let's all work to defeat antisemitism in 2020!"

Synagogues and shops in London sprayed with anti-semitic graffiti during Hanukkah