Gardaí suspect a faulty television or electrical appliance may have been to blame for the horrific fire at the Clondalkin apartment block.
AnneMarie O'Brien (27) who was seven months pregnant, her daughter Paris (2) and three-year-old Holly O'Brien were killed after the fire broke out at an accommodation in Kilcronan Avenue, Clondalkin around 2.30am last night.
Jordan O'Brien (4) died later this afternoon as a result of his injuries.
Jordan and Holly's mother Biddy O'Brien, who was visiting the apartment, remains in a critical condition.
Emergency services were alerted to the fire in the early hours of yesterday morning. Fire engines from Tallaght, Rathfarnham, Dolphin's Barn and Donnybrook, as well as a fleet of ambulances from Dublin Fire Brigade and the National Ambulance Service, attended the Cluainin Cronan complex.
Three neighbouring apartments accommodating seven residents had to be evacuated.
At the scene yesterday, Garda Inspector Ken McLaughlin of Clondalkin Garda Station said Gardaí and Dublin Fire Brigade would carry out a full investigation.
He confirmed all four who died in the fire were in the one apartment at the time of the incident. A full technical examination is due to take place.
"We're at the scene of a terrible tragedy and I would like to express our sincere sympathies for the families of those that are involved in this incident," he said.
"At the moment, we're keeping an open mind on the incident."
Sources told the Irish Independent that gardaí are investigating if an electrical fault caused the fire.
"Gardaí are looking at the possibility that this was a faulty TV or electrical device which caused the fire," the source added.
Gardaí are appealing for witnesses to contact them at Clondalkin Garda Station on 01-666 7600, the Garda Confidential Line 1800 666 111 or any Garda station.
Yesterday, Taoiseach Enda Kenny issued a message of condolence to the victims.
"I want to tender our sympathy on the death of a young mother and [the children] who lost their lives from smoke inhalation in a fire early this morning, and to the others who have been injured," he said.
Children's Minister Katherine Zappone said her thoughts and prayers were with all those affected by the horrific incident.
In a separate incident, a number of casualties were brought to hospital after a domestic fire on Dominic Street in Dublin's north inner city.
Four people were injured and several others were rescued. Three of the four were treated for smoke inhalation. The fire broke out around 3am yesterday.
Four units of Dublin Fire Brigade attended the scene, which was brought under control.