The Garda Commissioner, Mr Pat Byrne, visited the dig for the body of Jean McConville in Templetown, Co Louth, yesterday and pledged: "The digs will continue for the foreseeable future."
He warned, however: "The time will come when a decision will have to be made about the future of the operations. The passage of time has made the task of locating the remains very difficult."
The search for the bodies of the disappeared began after the coffin containing the body of Eamon Molloy was found in a graveyard in Faughart, Co Louth, on May 28th.
Gardai have been digging ever since, but have not managed to uncover the remains of other disappeared victims of the IRA.
They are now excavating at six locations in four counties.
Tredavent in Co Monaghan is the suspected grave of Columba McVeigh. Clogagh, Co Monaghan, is the suspected burial site of John McClory and Brian McKinney, who disappeared together in 1978.
At Coghalstown Wood in Co Meath it is suspected that the remains of Kevin McKee and Seamus Wright are buried. Also in Meath, Orinstown Bog is where they hope to find the body of Brendan Megraw.
Gardai in Wicklow are excavating at Ballynultagh, which is reputedly where Danny McIlhone is buried.
Gardai feel they have no reason to doubt the information given to the Commission for the Location of Victims' Remains. This is chaired jointly by former Tanaiste Mr John Wilson and the former head of the Northern Ireland Civil Service, Sir Kenneth Bloomfield.
The commission said: "We are remaining in close contact with intermediaries and the gardai to ensure the best possible information is available in the efforts to locate the remains of the victims."
A Garda representative said: "The search is continuing in all of the locations, with the areas being widened from those originally marked."
The work is painstakingly slow for gardai. They have to be very careful in their digging so as not to disturb the bodies.
The commission has remained committed to the task at hand and said: "We are anxious not to raise any false hope or expectation of early success. At the same time we are also anxious that the families should not become disheartened at this stage of what are, necessarily, slow and painstaking searches."
Mr Gerry Adams, president of Sinn Fein, said: "I am sorry that the bereaved families have been subject to the trauma and pain arising from the killings and from the long wait they have had until now to have the bodies returned."
The lack of success in the search has prompted strong criticism of the IRA and could affect Sinn Fein's election prospects.