The Real IRA, the republican group which bombed Omagh, is believed to be behind the 500lbs of explosives seized by police in a security operation in Northern Ireland.
The explosives were found when police stopped two cars in County Down.
If accurate, it will again call into question the ceasefire called by the Real IRA after the Omagh bomb atrocity in August 1998 in which 29 people were killed and more than 300 injured.
Three people who were arrested last night when the RUC stopped two cars on the main A1 dual carriageway near Hillsborough, about eight miles from Belfast, remained under interrogation in Belfast.
RUC Chief Inspector Ken Henning condemned the transportation of the home-made explosives.
He said: "It is something we would condemn without any hesitation. To transport that amount of explosives in a vehicle on a public road is highly dangerous. We condemn it outright."
The RUC was clearly delighted at having foiled an imminent attack.
Mr Henning said: "500lbs is a considerable device and would have caused considerable damage."
Speaking as police put the explosives, packed into eight polythene bags, on display at Grosvenor Road RUC Station in West Belfast, he refused to be drawn publicly on whether he believed the Real IRA was responsible.
He said only: "We believe the people responsible are connected to dissident republicans."
The seizure was made when the two cars, heading towards Belfast, were stopped by police and the bags of explosives found packed inside one of the vehicles.
Security forces believe the explosives were being taken to Belfast to be made into a bomb. Other items found in the two cars were taken away and were today being examined by forensic experts.
Other items seized when police searched a number of homes in West Belfast last night, were also being examined. No further arrests were made.Reuse content