The PSNI is staging round-the-clock security operations at a police station in Belfast to thwart a possible daylight mortar attack by dissident republicans.
A security source said police officers have been standing guard at the station since early February.
The Belfast Telegraph has chosen not to identify the location of the station but has observed officers carrying out foot patrols in its vicinity.
Officers have also been placed at the station's main entrances as a precaution.
The source revealed that the PSNI fears the possible attack may occur during the daytime in an attempt by dissidents to catch officers off-guard.
The source went into detail on how the security services believe the attack would most likely be airborne, and probably an improvised mortar device.
The PSNI has declined to respond, stating it does comment on operational matters.
The latest incident carried out by dissidents took place last December when a suspected grenade was thrown at a police car in west Belfast.
It follows a 12-month period of increasing activity from dissidents.
Last September a bomb - described as being in the "advanced state of readiness" - was made safe by ammunition technical officers after it was found in the Creggan area of Londonderry.
A similar attack took place two days earlier which resulted in the PSNI making safe a mortar bomb that had been left close to a police station in Strabane.
Last August dissidents used a hoax device to lure police officers and soldiers to a remote rural location at Wattlebridge near the border in Co Fermanagh and then exploded the real bomb.
Chief Constable Simon Byrne later laid the blame on Continuity IRA terrorists for the potentially lethal incident.
The previous month dissidents tried to murder police officers during an attack in Craigavon, Co Armagh, with a device discovered on Tullygally Road.
In July 2019 the New IRA claimed responsibility for a bomb placed under a police officer's car at Shandon Park Golf Club in east Belfast.
The PSNI later released a statement which placed the blame on "violent dissident republicans".
The latest PSNI security bulletin has revealed there has been an increase in the number of shooting incidents, bombing incidents and paramilitary-style attacks between March 2019 and last month.
It also recorded one security-related death - the murder of journalist Lyra McKee, who was killed by a bullet fired by dissidents during rioting in the Creggan in Derry.
Also in March dissidents posted five explosive devices posted to locations across the UK, including one sent to Glasgow University
Mark Lindsay, chair of the Police Federation of Northern Ireland, said yesterday that while he would not comment on the police station threat, any attempt by dissidents to launch an attack is to be "roundly condemned".
"We need an all-out effort by society to isolate such extremism and help the PSNI bring these people before the courts," he said.
"Officers are resolute in their determination to serve society and it is intolerable that in 2020 we still have to deal with such threats to our police officers."
The declining number of Catholic police officers in the PSNI has led to a recent recruitment drive by the organisation in a bid to encourage new recruits, particularly from a Catholic background.