Counter-terrorism police are investigating after 'Punish a Muslim day' letters were distributed to homes throughout the UK.
People in London, the West Midlands and Yorkshire have reported receiving the shocking letter.
The letter encourages people to harm and commit crimes against Muslims on April 3 and publishes a sickening point-scoring system of punishments.
People have been left horrified after a letter was sent to UK homes describing 'Punish a Muslim' day on April 3
The horrific letter encourages people to 'help turn things around' as it claims that Western Europe is being 'overrun'.
The point scoring system ranges from 10 points if you 'verbally abuse a Muslim' to 2500 points if you 'Nuke Mecca'.
Other sickening acts include 50 points for throwing acid in a Muslim's face and 1000 points for bombing or burning a mosque.
Counter-terrorism police are now investigating the letter after the Metropolitan Police, West Yorkshire police and the West Midlands police all received complaints.
The Counter-Terrorism Unit said in a statement: 'Police are investigating a number of reports of potentially malicious communications sent to individuals across the UK.
'Officers are currently investigating the full circumstances.
'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.'
This was the letter sent to several homes around the UK, including a score sheet of acts the writer encouraged people to perform against Muslims
Anti-racism groups have also expressed their horror at the leaflets, which direct anyone with questions to the HM Courts & Tribunals Service.
Campaign group Tell Mama UK said: 'We have been sent several reports of the 'Punish a Muslim Day' letter in London, the Midlands, and Yorkshire.
'We are working closely with the relevant police forces on this matter which is being treated with the utmost seriousness.
'It is essential that all letters and envelopes are kept and handled minimally to preserve evidence for the police to investigate.
'Incidents like this are rare but we urge vigilance and calm as we remind Muslim communities that our confidential support service is available to assist in this matter.'
The hate-filled letter says: 'Sheep follow orders and are easily led, they are allowing the white majority nations of Europe and North America to become over-run by those who like nothing more than to do us harm and turn our democracies into Shaira led police states.'
Bradford Councillor Riaz Ahmed received a letter to his business and expressed his shock at the contents
A Metropolitan Police spokesperson said that the letter is being investigated: '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.'
Police in Bradford have acknowledged they are investigating reports of the letters.
Councillor Riaz Ahmed, a Lib Dem in Bradford, West Yorkshire, said he received the letter to his business address.
He said: 'It was not addressed to anyone, just the address and postcode as if it was sent out randomly. It has a second class stamp on the plain white envelope and the frank mark is Sheffield. It was posted yesterday.
'It seems strange that anyone would send something like this to an address in a predominantly Muslim area. When I opened it and saw the content I was horrified.'
He said he believed the letter had been sent out by a group with the 'intent of alarming people' and 'to stir up racial hatred'.
Councillor Ahmed said: 'It goes on to ask if you are a sheep and 'are allowing the white majority nations of Europe and North America to become overrun by those who would like nothing more than to do us harm and turn our democracies into Sharia led police states'.
'They must be disaffected people to do something like this not knowing whose hands it may end up in.
'My main concern is that it could get into the hands of other disaffected people in Bradford who just need that push to act. Some people may look at is at a sick joke. I don't. I am alarmed by its content especially where it mentions acid because of all the recent reports in the media of acid attacks.'
This is the full sickening list of acts on the score sheet, as well as an explanation of the owner's motives
He added: 'It is shocking that anyone would even think of putting something like this together and posting it out knowing that it could potentially cause a lot of upset and harm.
'I am passing this to the police straight away and will encourage anyone who receives one to do the same.
'I don't really want people to be a concerned with these and the best advice I can give is for them to pass the letters if they get them to the police and then ignore them.'
Several people took to social media to express their shock and disgust at the vile letter
Counter-terrorism police are encouraging anyone who has received a letter to send it to their local police station
The letter bears an image similar to the royal coat of arms.
There is also an image of a dagger with the letters MS, suggesting it is linked to so-called Muslim Slayer who targeted mosques in London and the United States last year with similar threats.
A spokesman for West Yorkshire Police said: 'Police are investigating a number of reports of potentially malicious communications sent to individuals in the Bradford area. Officers are currently investigating the full circumstances.'
Anyone with any concerns about a communication they may have received should contact police on 101.