The Commission for the Location of Victims' Remains has confirmed that what is believed to be human remains have been uncovered just inside the border.
A statement said: 'The recovery is ongoing and the formal identification process will take some time.'
The Commission has been searching an area of Monaghan for the remains of Charlie Armstrong - one of the so-called disappeared
Father-of-five Charles Armstrong went missing on his way to mass in Crossmaglen in August 1981.
A number of searches undertaken by the Commission, including one in May 2002, and by the Armstrong family in an attempt to locate his remains have so far proved unsuccessful.
New information passed to the Commission in July of last year was described as a 'major breakthrough' and gave fresh hope to his family.
This information centred on a map depicting an area of bogland close to the border with South Armagh in Colgagh, near Inniskeen in Co Monaghan.
Mr Armstrong's daughter, Anna McShane, said in May the family remained hopeful that the latest search would locate the body of their father.
Mr Armstrong is one of 14 men and women abducted and killed by republican paramilitaries mainly the IRA during the Troubles. Five bodies have so far been recovered.
The IRA admitted in 1999 that it killed and buried nine of the disappeared - Seamus Wright, Kevin McKee, Jean McConville, Columba McVeigh, Brendan Megraw, John McClory, Brian McKinney, Eamon Molloy and Danny McElhone - in secret locations.
The bodies of Mr Molloy, Mr McKinney, Mr McClory, Ms McConville and Mr McElhone have been found.
Others who vanished during the Troubles include Gerry Evans, Robert Nairac and Seamus Ruddy, who disappeared in France and whose murder was admitted by the INLA.
The ICLVR was set up by the British and Irish Governments in 1999 and reports to the Northern Ireland Office in Belfast and the Irish Justice Department in Dublin.
In 2007, it brought in Geoff Knupfer, the investigative scientist who helped find the bodies of the victims of Moors Murderers Ian Brady and Myra Hindley, to spearhead a new scientific approach to the searches.
This included bringing in an archaeological 'time-team', made up of geophysicists who used ground radar, scanners, probes and cadaver dogs which detect human remains.
The Minister for Justice Dermot Ahern tonight thanked the Commission for its work in the last number of years.
'Their work is very valuable in bringing closure for the families of the Disappeared,' he said.
'It allows families the opportunity to say a final farewell by burying their loved ones with dignity and at family graveyards which they can visit and pay their respects.'
