Counter-terrorism police investigating the so-called "Punish a Muslim Day" letters have arrested a man on suspicion of conspiracy to murder.

The 35-year-old from South Lincoln is in custody in West Yorkshire following his arrest on Tuesday.

Lincolnshire Police said the man had been arrested on suspicion of sending a hoax noxious substance, sending threatening letters and conspiracy to commit murder.

Searches have taken place at a residential property in south Lincoln and an office building in the city centre.

It follows a number of reports of hate mail being received in March.

A police spokesman said: "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."