Two men arrested in Co Down in connection with the discovery of under-car booby-trap devices were still being questioned by detectives last night.
The men, aged 35 and 36, are well known to police, according to security sources, who linked the find to the "Real IRA".
They were arrested when armed police stopped a car on Tuesday night on a secondary cross-Border road near Newry known as the Fathom Line.
The devices were discovered some distance away in a second car which is believed to have been travelling behind. The driver escaped.
The Chief Constable of the Police Service of Northern Ireland, Mr Hugh Orde, blamed dissident republicans whom he said continued to pose a high security threat.
He did not speculate on the likely targets but the "Real IRA" has previously planted a booby-trap device under the car of a PSNI recruit.
Mr Orde said loss of life had clearly been avoided by the find.
Meanwhile, the Northern Secretary, Dr John Reid, has announced a new British government body aimed at fighting crime.
He said the agency would tackle "Wild West behaviour" on the streets.
The Law and Order Action Group will bring together Dr Reid, Mr Orde, the Attorney General and the Lord Chancellor's department.
"This is a group that will be looking for action rather than compiling some long reports for further consideration," the Northern Secretary said.DUP MP, Mr Nigel Dodds, expressed scepticism about the new group's effectiveness. Meanwhile, Mr Orde has announced he is redeploying 100 officers in Belfast to fight crime and deal with a shortage of detectives.
An advertising campaign to recruit more experienced detectives from police forces in Britain will also be launched.