A portion of more than six acres adjacent to the cemetery acquired several years ago will be used for new graves, which the diocese said will provide plots for the next 25 years.
Concerns were raised the continuing works in the cemetery could lead to disturbing unmarked graves of unbaptised babies and others, including adults who took their own lives.
The diocese on Wednesday said the section “will remain fully intact and untouched by the works”, adding that it has consulted with families and “memorialised the area with small black granite headstones”.
In addition, the area is surrounded by a laurel hedge “so that any unmarked graves in this section stay protected, undisturbed and respected”.
An “independent archaeological assessment, and a thorough review of burial records, have provided irrefutable scientific evidence that there are no existing burials within the expansion area”.
Gareth Hughes, the diocese’s chief operating officer, said it is “committed to preserving Milltown Cemetery’s role as a sacred and historic resting place for generations to come”.
He added: “These works will help secure vital burial provision for the next quarter century, whilst protecting existing graves and respecting the solemnity of the cemetery.”
“The Diocese is also eager to ensure that it upholds and promotes the heritage of Milltown, acknowledging that the cemetery is of huge historical importance. Our forthcoming digitisation project will open our records more widely and protect those records for generations to come.
“In particular, great care has been taken to protect and preserve the baby graves area, which holds deep emotional significance for so many families. The independent archaeological studies and review of records confirm there are no burials in the area of the new graves.”