Irish police intercepted "a significant explosive device" in a car travelling towards the border with Northern Ireland this week that they said on Friday was likely the work of nationalist militants opposed to British rule in Northern Ireland.
Police in the Republic of Ireland said detectives stopped the vehicle on Wednesday and called in the army's Explosive Ordnance Disposal team to examine the contents.
They said the driver of the vehicle, a woman in her 20s, was arrested and has since been charged in relation to the investigation. She is due to appear before a special sitting of Trim District Court, northwest of Dublin, on Friday.
A man in his 40s, who was also arrested, remains detained and is still being questioned.
"Certainly it was a significant explosive device, not just the seizure of components or pieces. It would have or could have potentially caused significant damage," Irish Police Commissioner Justin Kelly told a news conference.
"We know that there were a small minority of dissident republicans who did not agree with the Good Friday Agreement. I would describe them as radicalized republicans, and this is a threat that we're going to continue to face for some time," Kelly said.
Sporadic attacks by mostly nationalist militant groups, often attempted car bombings, continue in Northern Ireland almost three decades after the 1998 peace deal largely ended sectarian violence in the British-run region.
Some 3,600 people died during the conflict between nationalists seeking a united Ireland, pro-British unionists wanting Northern Ireland to remain a province of the United Kingdom, and British forces.
The vehicle was stopped close to the County Monaghan town of Carrickmacross, which is about 10 kilometres (6 miles) from the open border between the Republic of Ireland and Northern Ireland.
The New IRA militant group claimed responsibility for a car bomb that exploded outside a police station in Belfast in April, a month after another explosive device placed in a hijacked vehicle and targeting another station was made safe.

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