An internal message has been sent to all serving police officers and PSNI staff warning that dissident republicans are threatening their families.
Republican group Arm na Poblachta (ANP) has said that relatives of police officers are now being treated as "legitimate targets".
It is believed to be the first time an armed republican group has directly threatened civilian families of serving PSNI officers.
The chilling threat came as the hardline group also claimed that a device left under an off-duty PSNI officer's car in Co Derry had fallen off on Sunday.
It comes almost two weeks after the New IRA shot and seriously injured senior detective John Caldwell near Omagh.
Read more:
- Who are republican group Arm na Poblachta?
- New IRA deny link to loyalism over John Caldwell attack
On Monday the PSNI sent an internal message to all serving officers and staff warning that the threat had been received.
The intervention came after ANP made the threat in a statement to The Irish News using a codeword.
"We are now looking at the families of PSNI officers as legitimate targets," the ANP statement said.
"The PSNI have targeted republican sympathisers, now republicans will target family members of PSNI officers."
The Irish News understands the threat does not include the children of serving officers.
Speaking to The Irish News on Monday, Assistant Chief Constable Mark McEwan said the contents of the message to staff confirmed that the threat had been received and sought to "reassure that we are looking at the threat and seeking to corroborate it".
"We are taking it seriously and just remind people to take reasonable steps around their security on and off duty," he said.
"They are well used to these sorts of messages anyway.
"Any specific concerns, we will deal with those."
Mr McEwan said police had established a 'gold group', a co-ordination group, to look at the threat and other recent activity.
In March last year the security threat level was lowered from severe to substantial, meaning attacks are likely.
Mr McEwan said that while the threat level is currently under review, that is unconnected to the recent wave of activity.
"It's under review, MI5 review it, they review it every six months anyway, so that was happening anyway.
"More so because they do that twice a year rather than in response to this."
In a statement to The Irish News, ANP also claimed that the device had fallen off a car driven by a PSNI officer in the Oeghill Hill Park area of Lettershandoney, near Derry, on Sunday.
However, the PSNI said on Monday that nothing was found.
"Extensive searches have been conducted, however, nothing untoward has been located at this time," it said.
The anti-agreement group has also claimed that a device found in the Waterside area of Derry last month was left by its members.
A major security alert was launched after masked and armed men unsuccessfully attempted to hijack a car in Hollymount Park on February 17.
The following day a suspicious device, which police described as viable, was discovered in the Corrody Road area of the city, near the grounds of Doire Trasna GAA club.
The group claims two phone calls were made to a charity "on the night the operation was abandoned", adding that the device was partially disassembled.
"We made sure the device was secure before we left the area," a statement said.
DUP leader Sir Jeffrey Donaldson condemned the threat against families of police officers.
“It is hard to comprehend the mindset of those who would issue a threat against the families of our police officers,” he said.
“No-one should face such a threat because of their career and neither should their family.
“I know the whole community will stand united against those who would seek to drag us back.
“Those responsible for such threats must be brought to justice and it underscores the need to support the PSNI, both vocally and by pressing the Government to tackle the budget shortfall within policing.”
Sinn Féin policing spokesman Gerry Kelly said: “Reports that the Arm na Poblachta group has issued threats to the families of police officers is absolutely despicable.
“They should publicly withdraw these disgraceful threats, any other threats against police officers, and any intended attacks against anyone. They should pack up and go. There is no place for these groups in our communities.
“Some of these groups are heavily involved in criminality and have strong links to loyalist gangsters and other criminal gangs whose actions are a scourge on our society.
“Anyone with information on the people behind these threats should pass it on to the police.”
Read more: Who are the New IRA?
