A claim by the lobby group campaigning against the development of the M3 near the Hill of Tara that another potential national monument had been discovered in the path of the motorway has been denied by the National Roads Authority.
In a statement TaraWatch said that archaeologists working for the NRA had uncovered two stone souterrains, or underground structures, approximately 10 metres apart.
Cap stones have been removed and it is possible to see down into one of the chambers, according to TaraWatch.
However, the roads authority said at the weekend that the discovery was not a new one and involved features quite commonly found around the country.
A "souterrain" refers to an underground chamber, often found in the late Iron Age. Activists claim there may be many more underground chambers and passages as the area is being excavated for the first time.
The site lies approximately 80m northwest of the recently discovered henge in Lismullen, which was declared a national monument by Minister Roche.
TaraWatch claimed they had secured the area and would "protect" it by forming a circle around the site while reports are made to the National Museum and the Minister for the Environment, John Gormley.
The campaign group believes the find may constitute a "material change in circumstances", which the Minister said he would need before revisiting the issue of whether or not to reroute the M3 motorway.
The organisation has called for all work to cease immediately and said this is the case when a national monument is discovered during the course of roadworks, according to section 14 of the National Monuments Act.
The legislation also requires that the monument must be reported to the Minister for the Environment.
TaraWatch learned of the site while inspecting excavations on Friday evening, after archaeologists went home and left the site unguarded.
Laura Grealish of TaraWatch said that "this is a spectacular underground complex of chambers and connecting passages, with very high quality stonework". Vincent Salafia, also of TaraWatch pointed out that "we are reporting this discovery to the Minister and the National Museum this morning".
"We want to know if the National Roads Authority reported the discovery to the Minister or the museum, and if not, why not? The site is without doubt a significant new national monument."
Meanwhile, the National Roads Authority is becoming embroiled in a wider controversy about its proposal to take over responsibility for more of the roadways around the country
Hitherto, the NRA has only maintained responsibility for all the major national routes.
Details of the latest move, circulated to local authorities, were revealed during the past week in Co Monaghan.
It has led to a decision by local councillors to lodge a strong protest this week with the newly appointed Ministers for Transport and Environment.