A 13-year-old boy was punched in the stomach and subjected to anti-Semitic abuse on a bus.
He was attacked while travelling towards Stamford Hill, north London, at about 11:45 GMT on Sunday, a neighbourhood watch group said.
The Met confirmed it had received a report of anti-Semitic abuse and an assault taking place on a bus in the Stamford Hill area.
A spokesman said no arrests had been made and inquiries were continuing.
The tweet posted by the Shomrim group said a male hit the boy, who was Jewish, and shouted: “You stupid Jews think you own the world.”
There were no reports of any serious injuries. Police are appealing for witnesses.