Northern Ireland's environmental watchdog is investigating illegal dumps containing waste which is suspected to have originated in the Republic.
The investigation comes as environmentalists and politicians warn that the illegal dumping of waste from the Republic in the North is becoming a major environmental problem.
The closure of many landfill sites across Ireland and the major rise in the cost of disposal at legal landfill sites in the Republic has seen a huge rise in the illegal dumping of waste in the North.
The Environmental Protection Agency (EPA) has also said that cross-Border illegal waste activity will be examined as part of a major new study by the agency into the extent of illegal dumping and disposal in Ireland.
Many of the sites are located in Border regions, but illegal waste from the Republic has been found as far north as Coleraine.
Yesterday, Northern Ireland's Environment and Heritage Service confirmed it was investigating some sites where household and commercial waste from the Republic has been dumped.
A spokesman for the service said a number of files had been prepared for the Director of Public Prosecutions in Northern Ireland. He refused to comment further, claiming it could prejudice any future cases.
Ms Lisa Fagan, of the Northern Ireland office of Friends of the Earth, said the group had collated information on a series of sites across Northern Ireland which contained waste from the South illegally dumped there.
In one site in Garvagh, near Coleraine, Co Derry, bags from a waste company from the greater Dublin area were found.
The site, which was licensed to accept only builders' rubble and plastic, lost its waste license last year.
"There's a lot of waste coming from the Republic," Ms Fagan said. "We are aware of sites where waste from as far away as Tipperary, Wexford and Limerick has been found. It's coming into all of the six counties. In the Garvagh site, there was over 100,000 tonnes of rubbish, a lot of it from the Republic."
Mr Thomas O'Reilly, a Sinn Féin councillor in Co Fermanagh, said six illegal dumping sites had been identified in recent months in the county, and were currently under investigation.
"The local authority, Fermanagh District Council, has been trying to identify the sites," he said.
"It's an ongoing problem, and it will continue unless there is a fundamental review of how waste is collected and treated in the Republic."
Operators can earn up to 5,000 a load in refuse collection fees. However, they can be charged as little as £300 sterling for each load dumped at an illegal site.
Areas in Co Tyrone have also been affected by illegal dumping, with waste from the south-east located at a site in Strabane last October.
More recently, another site has been uncovered in Co Tyrone close the Monaghan border in the Corleaghan area, where waste from Co Donegal has been found.
Donegal County Council said yesterday it has not been contacted by any of the environmental authorities, but pledged full co-operation with any investigation.