Anti-Semitic graffiti has been daubed on a synagogue and several shops in north London during the Jewish festival of Hanukkah.
The Star of David, a Jewish holy symbol, and 9 11 were spray-painted in Hampstead and Belsize Park on Saturday, referencing a conspiracy theory.
South Hampstead Synagogue was among the premises targeted, with reports being made to police from about 23:30 GMT.
Police are treating it as a racially motivated hate crime.
The graffiti references an anti-Semitic conspiracy theory that Jews are responsible for the 9/11 terror attack.
The vandalism was carried out six days after the start of Hanukkah – one of the biggest festivals of the year for Jewish people. No arrests have been made.
Mayor of London Sadiq Khan said on Twitter: “This makes me sick to my stomach” adding that “anti-Semitism like this” had “no place anywhere and certainly not in London”.
He also said that residents could expect more police patrols in the area.
Conservative councillor for Hampstead Oliver Cooper said he spent Sunday morning patrolling the neighbourhood after “appalled” residents alerted the Community Security Trust 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.”
Mr Cooper said he came across the graffiti in nine places, and others also posted photographs of the markings on Twitter.
Labour MP for Hampstead and Kilburn Tulip Siddiq said the vandalism was “unbelievable, senseless, disgusting anti-Semitism at the heart of our community”.
“I am in touch with Camden Council and Borough Commander (Raj) Kohli regarding clean-up and attempting to find these criminals – we must all stay vigilant in order to continue the fight against this hatred,” she said.
Insp Kev Hailes, of the Met, 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.”
The graffiti was seen being removed from shop windows on Sunday afternoon.