Gardaí have opened a double murder investigation after a young boy and his great-aunt were killed in a suspected petrol bomb attack on a house in Co Offaly.

The murder victims were named locally last night as Tadhg Farrell (4) and Mary Holt (60).

Another women, who is in her 50s, was in critical condition in hospital having suffered extensive burns in the blaze at Castleview Park, Edenderry. It is understood she is Ms Holt’s sister and the deceased boy’s grandmother.

Gardaí believe a petrol bomb or similar was thrown into the house on Castleview Park in the town just before 7.45pm. The fire engulfed the end-of-terrace property, in a local authority estate. It appears the deceased were trapped in a downstairs room as a result of the fire.

After the blaze was brought under control the remains of Ms Holt and her grandnephew, Tadhg, were discovered inside the charred property.

Gardaí suspect criminals involved in the drugs trade in the Midlands were behind the firebombing.

Minister for Justice Jim O’Callaghan condemned the attack, which he said had “sadly resulted in the loss of two lives including a young child”. He added there “is no place in a civilised society for such heinous violence. I join An Garda Síochána in appealing to anyone with information to come forward”.

Supt Liam Geraghty said gardaí believe the house “was attacked” by one or a number of perpetrators and the fire deliberately started. He added it was “a reckless, callous and murderous attack on a family home”.

Cllr Claire Murray (FF), who represents the Edenderry local electoral area, extended her sympathies to the family of the victims and those living in the Castleview estate. “It is hard to put into words how devastated people are. The loss of such innocent life is inexcusable. Edenderry is a darker place today,” she said.

The remains of the victims were removed from the house on Sunday and underwent postmortems by the Assistant State Pathologist Margot Bolster at the Midland Regional Hospital Tullamore. The house, which was gutted by the fire, was sealed off and declared a crime scene.

The Garda Technical Bureau carried out an examination as part of the murder inquiry and was expected to return on Monday. Gardaí have also carried out door-to-door inquiries. The process of gathering CCTV footage, in the hope it may have captured the attackers going to and from the scene, has also commenced.

Garda sources said the incident was probably intended as an intimidatory attack and they did not believe the people at the property were the intended targets.

Gardaí have opened a double murder investigation, led by a senior investigating officer at Tullamore Garda station. Detectives believe local people have information about the incident and have urged them, or anyone who was in the area at the time, to come forward.

As part of the investigation, gardaí are examining other violent incidents in the Castleview area in a bid to determine whether there are links to Saturday’s fatal fire. The incidents in recent years include a petrol bombing, where it is believed the wrong house was targeted, and the discovery of a suspected improvised explosive device.

An emergency-services team comprising personnel from the Offaly Fire and Rescue Service, National Ambulance Service and gardaí rushed to the scene after the alarm was raised. However, although the fire was eventually brought under control, efforts to rescue those trapped inside were not successful.

As part of the murder inquiry, gardaí are keen to speak to anyone who was in the vicinity of Castleview Park, or nearby roads, between 7pm and 8pm on Saturday.

Anyone who was recording footage in the area at the time, including drivers recording dashcam, was also urged to make that footage available to the investigation team.