Arlene Foster has said she is disappointed that Sinn Féin's Stormont leader is attending a commemoration for eight IRA members killed by the SAS in the North.
Michelle O'Neill will address a republican parade and memorial event on Sunday marking 30 years since the ambush by elite troops in Loughgall in Co Armagh.
DUP chief Mrs Foster met Irish language students in the North as part of a bid to learn more about the language as part of efforts to restore devolved powersharing with nationalists.
She said: "It is disappointing that when I am trying to make this a shared place for everybody in Northern Ireland that other leaders are doing things that frankly are wrong and backward-looking.
"I am thinking of what is happening in Loughgall on Sunday and I think that is something that Sinn Féin needs to reflect on because we have heard a lot during the election about respect and they need to understand what that means in terms of the past and indeed in terms of the future as people look to the future here in Northern Ireland."
The SAS intercepted the IRA unit as it launched an attack on a police station in the village in May 1987 and riddled its van with bullets.
Sinn Féin considers those who died as martyrs; many unionists consider them as terrorists.
Controversy has long surrounded the ambush, which also killed a bystander, amid claims the gunmen continued to fire on a number of the IRA men with heavy machine guns as they lay wounded on the ground.
A lawyer for the bereaved has claimed the servicemen acted excessively.
The DUP has accused Sinn Féin of demonstrating little respect to the victims of IRA terrorism, choosing instead to describe a group of men who went out with the sole intention of murder and mayhem as martyrs.
The IRA members killed were Jim Lynagh, 32; Padraig McKearney, 32; Gerard O'Callaghan, 29; Tony Gormley, 25; Eugene Kelly, 25; Patrick Kelly, 32; Seamus Donnelly, 19; and Declan Arthurs, 21.