The IRA has used go-betweens to pass on information about the burial sites. But officers have warned that it could be some time before any bodies are recovered.

Superintendent John Farrelly said: "The information we have received indicates that the remaining bodies will be located at these particular sites.

Denis Murray in Belfast: A grim task

"But I have to emphasise that is going to be a difficult, prolonged and protracted investigation leading to the actual recovery of the bodies. People will have to be patient."

Car park was given a Tarmac surface less than a decade ago

After more than 24 hours of excavations at three sites a special squad of police and pathologists reported no progress.

Arrangements are being made to look after relatives visiting sites being investigated in Counties Louth, Wicklow, Meath and Monaghan.

One body was recovered on Friday and on Saturday Garda started digging at a car park next to the beach at Carlingford, County Louth.

Seamus McKendry: "It's the final chapter in years of agony for our family"

The victim believed to be buried there is Jean McConville - a mother of 10 who was seized by the IRA from her home in Belfast in 1972.

Seamus McKendry, Mrs McConville's son-in-law, has been joined by other family members at the site. They share his worry that she might never be found.

The car park has been given a Tarmac surface within the last decade, and Mr McKendry said: "It's absolutely incredible that someone could pinpoint somewhere on a sand dune after 26 years."

Since her death all the children have been together just once, but they have reunited again to monitor the progress of the police.

Helen McConville faces an anxious wait for news of her mother's remains

A spokesman said they would stay together until Mrs McConville was found and the family could at last give her a proper funeral.

Relatives of the other victims have been making their way to the different dig sites as well.

Officers leading the operation have acknowledged they are relying on the memories of IRA personnel about events dating back more than a quarter of a century.

Another police source said the extent of the task confronting them was becoming clear. "The recovery of the first body, of Eamon Molloy, on Friday, was relatively simple, he had been left above ground in a coffin. But the rest of the operation will be much harder."

Ireland Correspondent Denis Murray: "The information is precise and detailed"

A senior police officer said excavation work was being carried out on three sites: Templetown for Jean McConville, near Blessington, Co Wicklow; and close to the Irish border in Co Monaghan, where it was indicated that John McClory and Brian McKinney had been buried.

Three other sites were cordoned off but work was not expected to start until excavation ended at the current digs, said Chief Superintendent Mick Finnegan.

One of the sites near Kells, Co Meath, was understood to be the burial place of Brendan Megraw.

Another near Navan, Co Meath, was said to contain two bodies.

Mr Finnegan said digging would continue until nightfall and resume in the morning.