Four children, including a baby, have been taken to hospital after fireworks were thrown into a building housing people applying for international protection.
It happened in Drogheda, County Louth, on Friday night.
Gardaí (Irish police) were alerted by the fire service to a blaze at the property at about 20:15 local time. The fire has since been extinguished.
An adult was also taken to hospital.
Ireland’s Justice Minister Jim O’Callaghan described the incident as “a terrifying ordeal for the women and children living there”.
“Fireworks were thrown into the building, causing a fire and putting lives at risk,” he said.
He said alternative accommodation is now being sourced for the residents affected.
“There will be serious consequences for those responsible,” he added.
Taoiseach (Irish prime minister) Michéal Martin has condemned “in the strongest terms, the deeply disturbing incident”.
“To put vulnerable families, including young children, at risk is abhorrent and has no place in our society,” Martin said.
“Our thoughts are with those affected by this horrifying experience.”
A Garda statement said: “This was an extremely dangerous act endangering the lives of the residents, including children, who were in their home at the time.”
The scene has been technically examined and a senior investigating officer is leading the investigation from an incident room at Drogheda Garda Station.
Gardaí have appealed for information.