The inquiry, set up in 2013 and chaired by Sir Anthony Hart, has been examining 13 institutions and the child migration scheme to Australia.

On Monday, Sir Anthony announced an extension to his remit to include Fort James and Harberton House in Londonderry, which have both closed, and Hydebank Young Offenders’ Centre in south Belfast

He said: “Today we wish to announce that we are adding three more institutions to the list, and one individual, bringing the total of homes and matters to be investigated to 18. 

“Fort James and Harberton House, both statutory homes in Londonderry, will be dealt with together in module five which will take place next month.

“It will be followed by module six which will examine issues arising from the actions of Fr Brendan Smyth in a number of homes in Northern Ireland, actions which have been described by a number of witnesses who have already given evidence to the inquiry.

“This module will follow directly after module five, and will complete our schedule of public hearings for the first half of this year.

“At the beginning of September we will resume public hearings with module seven, during which we will hear evidence relating to three of the institutions we have already announced, namely St Patrick’s Training School, Lisnevin Training School and Rathgael Training School.

“We are adding Hydebank Young Offenders’ Centre to the list of institutions we are going to investigate, and it will also be considered in module seven, which we anticipate will last until November.

“It will be followed by module eight which will deal with two homes run by Barnardo’s, Sharonmore and Macedon, and that module will take us up to the end of this year.”

Smyth, who was at the centre of one of the first clerical child sex abuse scandals to rock the Catholic Church in Ireland, was eventually convicted of more than 100 child abuse charges on both sides of the Irish border.

He died in prison in 1997 following a heart attack.

The HIA module focusing on his actions will begin on 22 June and is expected to conclude by the end of the month.

In total, the inquiry is expected to hear from more than 300 witnesses during the public evidence sessions.

The inquiry is examining the extent of wrongdoing in a number of institutions - including industrial schools, workhouses, and borstals - between 1922 and 1995. Many of which were run by religious orders.

Victims have alleged they were subjected to physical, sexual and emotional abuse.

The inquiry has been granted an additional year to carry out its investigations and is expected to report its findings in January 2017.