Enda Kenny has described the deaths of two elderly men whom he knew well, in Castlebar, Co Mayo as "an act of savagery".
The Taoiseach says he spoke to Gardaí and they are following a number of lines of inquiry.
The bodies of the two brothers, who were in their 60s and 70s, were discovered at their house on New Antrim Street in Castlebar.
A home help assistant - who looked after the men - alerted Gardaí at around 7 o'clock this morning.
The Taoiseach, who is from Castlebar, says the brothers were well liked and never harmed anyone in their lives.
"I was shocked this morning to get a call from my own town where there's been a brutal and savage murder of two men that I knew well, two brothers," he said.
"[They] were residents of the street where my office is for very many years, and I find this is an act of savagery."
Paul Dunne, a cousin of the two men, says they were harmless individuals who kept to themselves.
"They done their own thing, they didn't do no harm to anybody," he said.
"They'd never complain about pains or aches. That's how you could sum it up."