A fire which killed two Polish men after sweeping through their house in Belfast was a tragic accident, authorities said today.
The migrant workers, both in their early 20s, were among four people trapped as flames engulfed the two-storey property in the Tiger's Bay area in north Belfast.
Amid fears the blaze could have been deliberate, police and fire chiefs launched an urgent inquiry to discover its cause.
They have established that it started in the kitchen area of the building on Camberwell Terrace.
Police Service of Northern Ireland chief superintendent Gary White, commander for north and west Belfast, said: "Whilst we are at the very early stage of the investigation, all of the indications are pointing towards this being a very tragic accident."
A smoke alarm was discovered among the debris, although investigators did not say whether the device was in working order.
Efforts were continuing tonight to contact the families of the men who died.
Six eastern Europeans, including one holidaying in Belfast, were in the house when the blaze broke out.
Fire chiefs said crews on the scene within minutes of being alerted were confronted with a harrowing scene. Search teams using breathing masks and extension ladders located three people and got them out of the house. They were taken to hospital for treatment, where one later died.
Another man was found dead in the house. Two men had managed to escape the building before the Fire Service arrived just after 3am.
Area commander Chris Kerr described his officers' battle to get to the victims.
"Crews were met by a harrowing sight, a two-storey mid-terrace house well alight on both floors, thick black smoke issuing from every doorway and window and one person calling for help from a window of the upper floor."
He said that person was rescued along with two others by fire officers who used breathing apparatus to get into other upper rooms.
Adjoining houses were evacuated during the blaze which was later brought under control.
One of those rescued remained in hospital and two others have been released after treatment.
Meanwhile, a major gorse fire on Black Mountain above Belfast is thought to have been started maliciously.
Up to 50 acres of National Trust land was affected by a fire which had two separate seats.
National Trust warden for the area Dermot McCann said he believed the fire was started deliberately.
"This is an ongoing set of malicious fires that have been lit on the mountain, and it has been ongoing since Easter."
He added: "These fires can result in the loss of life, never mind habitat and animals on the site - we have cows on the property, it is an open farm, and we have about 25 horses as well.
"It is endangering everyone on the mountain - and it also puts the lives of the emergency services at risk. Depending on which way the wind goes, it can really get very bad very quickly."
Three fire crews were sent to the mountain to tackle the fire and an investigation was due to be carried out today to try to establish whether Mr McCann was accurate in his belief it was another malicious blaze.