The New IRA has developed a different kind of highly dangerous explosive bomb, police in Northern Ireland warned.
It involves a pressure plate designed to detonate when a car drives over it.
The method was used by dissident republicans opposed to the peace process who targeted an off-duty officer in Londonderry in February this year.
Police Service of Northern Ireland (PSNI) detective superintendent John McVea said: "The pressure plate is a crude method of detonation.
"So not sophisticated, but a very effective means of detonation.
"The New IRA have access to high explosives - which is concerning."
He said that pressure plate method had been seen just once before in the Derry area.
The senior detective said the new device had been developed because of the difficulty of attaching booby-trapped bombs to the underside of cars, traditionally used by dissident republicans to target officers at their homes or in the community.
That was historically done using magnets but modern cars are made using more plastic, Mr McVea said.
The bomb itself is a box of explosives wrapped in tape and placed under a car. The pressure plate detonator is activated when a car wheel drives over it.
Police are on high alert for more attacks from dissidents opposed to the peace process.
The detective said: "It is concerning that they have access to high explosives and have the skills to develop their own homemade method of detonation by way of the pressure plate design."
Mr McVea said a pressure plate detonator was used in February to target the vehicle of an off-duty officer in Londonderry in the driveway of his home.
It failed to explode and was discovered hours later on the driveway, exploding while it was being examined.
The only other case was in a linked attack at Ballyarnett village in Londonderry in October 2014 when a pressure plate was left under a mat with the intention of luring officers to stand on it.
The new IRA was formed in 2012.
Several dissident republican organisations said they were unifying under one leadership.
It is believed to be the largest of its kind and has been linked to a number of attacks on police.