An eight-year-old girl was among three members of the same family found dead in a house in Ballymena.
The family was originally from Poland, although it is understood the child was born in Northern Ireland.
The honorary consul of Poland in Northern Ireland said the family had been settled here for some time.
Jerome Mullen said: “I’ve never experienced such a tragedy in all my 18 years as honorary consul.”
A murder investigation was launched after the three people – a man, a woman and the girl – were found at a house on the Cullybackey Road at 09:00 BST.
Police have said the cause of their deaths has not been formally established and post-mortem examinations are to be carried out.
However, they said they did not believe there was an ongoing risk to the public and they were not seeking anyone else in relation to the deaths.
Mullen said he was “absolutely shattered and devastated” by the news.
“The Polish community has been living in Northern Ireland and has been very settled for 20 years,” he said.
“This is the worst tragedy that I’ve come across in my experience.”
He added that Poland had a full diplomatic presence in Northern Ireland and the consulate was providing assistance and support to the family circle.
At the scene on Tuesday morning, BBC News NI’s Kelly Bonner said the area was subdued.
“The police cordon is still in place on the Cullybackey Road,” she said.
“This is quite a quiet area, it is quite a rural road.
“For neighbours and people living in this community, they are still trying to come to terms with what has happened.”