Arlene Foster has said she is disappointed that Sinn Fein's Stormont leader is attending a commemoration for eight IRA members killed by the SAS in Northern Ireland.
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 Northern Ireland 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 Fein 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 Fein considers those who died as martyrs; many unionists 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 Fein 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.
Arlene Foster said Mrs O'Neill's attendance sent out a very primitive message about her attitude to building a shared society.
The Co Tyrone-born leader, who has a family republican background, has defended her presence at commemorations for IRA members killed by the SAS, urging there should be no hierarchy of victims from the decades of conflict and describing them as ordinary men in extraordinary times.
The SAS, with its tendency to rely on heavy firepower, was deployed in Northern Ireland in 1976 to target the IRA.
While it thwarted potentially deadly attacks the regiment has been accused by nationalists of operating a "shoot-to-kill" policy and was involved in several disputed killings.