Emergency services have been called to Didsbury Mosque, it has been reported.
The road around the mosque in Burton Road, Didsbury, Manchester has been closed.
A Greater Manchester Police spokesman said: “Police were called to the Manchester Islamic Centre, on Burton Road, in Didsbury at 11.40am. Officers received a call that there had been a threatening letter sent to the Islamic Centre.
“Police attended and, together with the fire brigade, are currently accessing the letter.
"At this stage it is being treated as low risk. Officers are expected to remain at the scene for the rest of the day."