Scotland Yard is investigating a possible hate crime after reports a letter encouraging people to "punish a Muslim" was posted in London.

The threatening letter, which has also been circulated online, urged its recipients to join a national day of violence against Muslims in April.

It asked people to carry out violent acts including verbal abuse, removing a woman’s hijab or head-scarf, physical assault and using acid as a weapon.

These were ranked using a points-based system, with the letter stating: “There will be rewards based on action taken”.

The Met Police confirmed on Saturday that it is investigating the letter and added that no one has been arrested.

A spokesman said: “Police are investigating a report of malicious communications in a letter having been sent to the occupants of a residential address in east London.

“A further report has been received from a member of the public in the SW4 area who received a copy of a letter through Whatsapp.

“The MPS does not tolerate any form of hate crime. If anyone believes they have been a victim of such an offence we would encourage them to report it to police so it can be fully investigated.”

Meanwhile West Yorkshire Police confirmed it had around six reports of letters advertising "punish a Muslim day" and said counter terrorism police were investigating.

A police spokesman said: "Counter Terrorism Policing North East are coordinating the investigation at this time and will consider any potential links to existing enquiries.

"Anyone with any concerns about a communication they may have received should contact their local police force."

Social media users in Birmingham have also reported receiving the letters.

Iman Atta, director of anti-Muslim hate monitoring service Tell MAMA, said: "This has caused quite a lot of fear within the community.

"They are asking if they are safe, if their children are safe to play outdoors. We have told them to keep calm, and to phone the police if they receive one of these letters."