Image copyright Pacemaker Image caption The bomb is detonated by a pressure plate like this one

Dissident republicans have developed a new kind of under-car bomb, the PSNI (Police Service of Northern Ireland) has warned.

It involves a pressure plate designed to detonate when a car drives over it.

The method was used by the New IRA when the group targeted an off-duty officer in Londonderry in February.

"The pressure plate is a crude method of detonation," said Det Supt John McVea. "Not sophisticated, but a very effective means of detonation."

Image copyright Pacemaker Image caption This bomb was used to target a police officer in Londonderry in February

He expressed concern that the New IRA had access to high explosives, and appealed for new information regarding the device found under the officer's car at Ardanleee, in the Culmore area of the city.

Police believe a similar pressure-plate device was used in an attack at Ballyarnett Village in Derry, in October 2014, when a bogus phone call was used to lure officers to the area.

What is the New IRA?

The new IRA was formed in 2012 after a number of dissident republican organisations said they were unifying under one leadership

It is believed to be the largest dissident republican organisation

The group is believed to have been responsible for a number of attacks since its formation, including the murders of prison officers David Black and Adrian Ismay.

Magnetic under-car bombs have been commonly used by dissident republicans to target police officers in the past.

Modern cars are made using more plastic, the senior officer explained, making it more difficult to attach a magnetic device.

The bomb itself comprises a box of explosives wrapped in tape and placed under a car.