Dissident republicans have issued threats against the security forces, drug dealers and foreign criminal gangs in a letter received by the Belfast Telegraph.
The letter sent to this newspaper from a group describing itself as "the republican movement" featured a sinister picture of three men in paramilitary attire, two of them brandishing automatic weapons.
The group said a recent spike in drug deaths had left it with "no other option than to take military action" against drug dealers.
The letter also said foreign criminal gangs involved in drugs, prostitution and human trafficking would be "seriously dealt with", mostly by "execution" or expulsion.
And it warned that "anyone who operates in the drug trade with loyalist paramilitaries will be dealt with".
Coming days after a series of security alerts in Londonderry, including a car bomb detonated outside the courthouse, the statement said it would "actively target Crown forces".
The PSNI said: "Police are aware of a letter of correspondence sent to a local media outlet.
"Officers will examine the content of the letter.
"We would urge anyone who may have any evidence of illegal activity to bring that information to the police."
Separately, two men aged 65 and 48 and a 61-year-old woman were arrested in the Springfield Road area of west Belfast yesterday on suspicion of dissident republican activity
The suspects were taken to Musgrave Serious Crime Suite for questioning. Dissidents have been linked to a series of incidents in recent days, including a car bomb detonated in Derry and four bomb hoaxes. Five people were arrested in the wake of last Saturday's explosion.
All were later released unconditionally.
The PSNI blamed the 'New IRA' for the blast.