A boy, a girl and a woman in her 40s have died after a shooting near Maguiresbridge in Co Fermanagh yesterday, police have confirmed.
A man remains in a serious condition at the Royal Victoria Hospital in Belfast.
Superintendent Robert McGowan confirmed that all four people were from the same household and suffered gunshot wounds.
The PSNI has begun a murder investigation and said detectives are "working at pace to determine the circumstances".
Two of the victims, a woman and a child, were pronounced dead at the scene on Drummeer Road.
The second child died later in hospital.
Police received a 999 called from someone inside the house appealing for help shortly before 8am.
Officers were despatched immediately from Enniskillen station around 13km away.
When they arrived at the property, they found four people inside with gunshot wounds.
They then called the ambulance service who despatched crews to the scene.
Watch: Supt Robert McGowan confirms all four people were from the same household
Police are not seeking anyone else in connection with the incident.
Police are treating this as a domestic incident.
One line of inquiry pursued by the PSNI is that what happened was a triple murder and attempted suicide.
Supt McGowan said the suspect has a "limited footprint" with police and that the incident happened in a "quiet, rural location".
He said he is aware that this incident will have sent "shockwaves of sadness throughout the community", adding that there will be a continued police presence in the area.
He expresed his "sympathy to family members and loved ones who are today left in total shock, and who will inevitably be struggling to come to terms with their unimaginable loss".
Supt McGowan said that it was a "very difficult" scene for police to attend.
He said that enquiries are at an early stage and asked for "patience as we work to understand the events that have taken place".
The PSNI appealed to anyone with information, CCTV footage or dashcam footage to contact them.
We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences
Deceased were 'active' GAA members in community
St Mary's Maguiresbridge Gaelic Football Club said the three people who died "were active and beloved members of our club".
In a statement on Facebook, the club offered its "heartfelt condolences to the families and friends of those impacted by the tragic incident which happened in our community this morning".
"We are working with the GAA at county, provincial and national level, to implement the Association's critical incident protocols.
"We will work closely with all appropriate services to ensure that those who require support at this difficult time can access it," the statement added.
St Patrick's Hurling Club, based in the village of Lisbellaw, close to Maguiresbridge, also said the deceased "were active and beloved members".
The club offered its "heartfelt condolences to the family and friends of all those impacted" and said it is working to implement the GAA's critical incident protocols.
"We will also work closely with all appropriate services to ensure that those who require support at this difficult time can access it," the club added on Facebook.
Fermanagh GAA also issued a statement in which it offered its "heartfelt condolences to the families and friends of those impacted by the tragic incident which happened in our community this morning" and said it is "thinking of and supporting" the two clubs.
Watch: DUP MLA Deborah Erskine says the community is in shock
Northern Ireland First Minister Michelle O'Neill said she is "absolutely heartbroken by the news from Maguiresbridge".
In a post on X, she said she has no doubt the community will come together and "support one another through this incredibly difficult time".
Deputy First Minister Emma Little-Pengelly described what happened as "just horrific beyond words".
"Truly devastating to hear of this terrible and violent event. My thoughts at this dreadful time are with the loved ones, family and friends but most of all for the tragedy of the lives cut off so cruelly," she posted on X.
UUP MLA for Fermanagh and South Tyrone Diana Armstrong said her "thoughts are with the families of those affected and with everyone in this rural local community as they come to terms with this tragedy".
She urged people to "allow space for the investigation to proceed and respect the privacy of those involved at this difficult time."
Sinn Féin MP Pat Cullen said she is in contact with the PSNI on the situation and urged people "to not speculate on the details of this tragic and shocking incident."
Speaking on RTÉ's News at One, she described the area as a "very, very close-knit, rural community, mostly a farming community, but one where everyone will know each other, so you can imagine how the people must feel here, learning this when they woke up".
Ms Cullen, who is a former general secretary of the Royal College of Nursing said her thoughts were also with the paramedics and doctors who arrived on the scene "and what it must have been like for them".
She said they are "so expert in what they do that they would have moved into that space of just immediately dealing with the injured people that they found in the home this morning".
"But when you come away as a nurse or a doctor or indeed a paramedic, it remains with you for an awful long time, if it ever leaves you, so my thoughts and prayers are with them," she said.
Secretary of State for Northern Ireland Hilary Benn said: "The news from Maguiresbridge is tragic and deeply distressing.
"My thoughts are with the victims, their relatives and the local community in Fermanagh.
"I would urge the public not to speculate and to allow the PSNI to continue their investigation."
Additional reporting PA
