Officers were called to an address in the Molly Road area of Derrylin, Co Fermanagh at around 7.20 am this morning.
Detective Superintendent Jason Murphy said: “Sadly we can confirm that three people have lost their lives in this fire.
“Emergency services remain at the scene and are carrying out an extensive examination of the property to establish the cause of the blaze and determine if any other persons have been involved.
“I would appeal to anyone who was in the area and who may have seen anything that could assist the officers investigating this incident to please get in touch by calling 101.”
Police say that at this stage it is not possible to say how the fire started.