Delays in progressing the trial of those indicted for the killing of Private Seán Rooney are "simply not acceptable" to the Government, Tánaiste Simon Harris has said.
Mr Harris said he would be conveying that message "in the strongest possible terms" during political meetings in Lebanon.
Private Rooney was shot and killed in Lebanon in December 2022.
Mr Harris will also visit Irish peacekeepers currently deployed in the country during his trip this week.
There are 339 Defence Forces personnel currently serving with the 125th Infantry Battalion which is part of the UN Interim Force in Lebanon, or the UNIFIL mission.
Last weekend, Israel carried out military strikes on targets in the region, which killed seven people, after rockets were fired into northern Israel by unknown Lebanese militants.
Mr Harris is expected to announce increased funding for local community projects in southern Lebanon - an area which was severely damaged in 14 months of war in 2023 and 2024.
During a series of political meetings, it is anticipated the Tánaiste will raise the Government's "frustration and concern" at the lack of progress in the trial of seven people indicted in the killing of Private Rooney.
Only one of the seven has been detained.
Mr Harris is expected to stress the need to deliver "accountability and justice" for the Rooney family.
Speaking to reporters before travelling to Lebanon, the Tánaiste said: "I am very much looking forward today to going to Lebanon to meet directly with Irish peacekeepers - 339 members of Óglaigh na hÉireann who are serving with distinction in a very troubled and difficult part of the world.
"I am very proud of Ireland's record in peacekeeping over many decades in Lebanon and it is important for me to have an opportunity to thank our troops directly, to hear from them directly and also to have a number of political meetings while there.
"I am looking forward to meeting the defence minister and the foreign affairs minister tomorrow where I will have an opportunity to raise the case of Private Seán Rooney.
"It is simply not acceptable to the Irish Government that it has taken so long to make progress in relation to the trial of those accused of the murder of Private Rooney and I look forward to conveying that in the strongest possible terms."
Additional reporting PA
