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 symbol, and "911" were spray-painted in Hampstead and Belsize Park, possibly referencing a conspiracy theory.
South Hampstead Synagogue was among the premises targeted, with reports made to police from 23:30 GMT on Saturday.
Police are treating it as a racially motivated hate crime.
The graffiti could reference an anti-Semitic conspiracy theory that Jews are responsible for the 9/11 terror attack.
It could also reference Kristallnacht, an organised nationwide attack on Jews which began in Germany on 9 November 1938.
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.
A South Hampstead Synagogue spokesman said: "This is a time for people of all backgrounds - of all faiths and of none - to stand united and show our determination that we do not tolerate prejudice, hate and division - on our streets or online."
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MP for Hampstead and Kilburn Tulip Siddiq, MP for Holborn and St Pancras Keir Starmer and Camden Council leader Georgia Gould released a joint statement, which read: "Camden is and always will be no place for hate.
"We stand together with all of our Jewish residents and our whole community in saying these cowardly pedlars of hate do not represent Camden and our values.
"We are proud to have a strong, vibrant Jewish community as part of our beautiful borough.
"This is not an isolated incident and we must all confront the rising tide of hate crime and anti-Semitism in the UK.
"Now is the moment to find the courage to confront hatred and prejudice wherever we see it."
Camden street cleaning teams are removing the graffiti "as quickly and sensitively as possible," they added.
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.
Ms Siddiq described the vandalism as "unbelievable, senseless, disgusting anti-Semitism at the heart of our community".
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.