"We understand that people may be concerned following this activity. However, we would like to reassure communities that this activity is a result of an ongoing, intelligence led investigation and was not in response to an immediate threat," the police said in a statement.
The 35-year-old man is suspected of sending the 'Punish a Muslim Day' letters, or as described by the police — "sending a hoax noxious substance under section 114(1)(a) and (3) of the Anti-Terrorism, Crime and Security Act 2001; Sending letters/communications/articles conveying a threatening message contrary to section 1(1)(a) and (4) Malicious Communications Act 1988; and conspiring and soliciting to commit murder contrary to section 4 of the Offences Against the Person Act 1861."
READ MORE: UK Police Investigating 'Punish a Muslim Day' Letters Received Across Country
Residents across the country have been reportedly receiving letters, calling for violent attacks against Muslims on April 3, 2018 and promising "rewards based on actions taken."
On March 12, Detective Chief Superintendent Martin Snowden, Head of Counter Terrorism Policing North East said the authorities "take religious hatred extremely seriously" and his "officers will be carrying out a full and thorough investigation in response to these reports."
Following the reported incident, an anti-racism campaign group took to social media to demand an end to Islamophobia in Britain and encourage people to show solidarity with British Muslims.
READ MORE: 'Buy Them Coffee & Cake': How to Celebrate the 'Love a Muslim Day' in Britain