Dissident republicans are making a “concerted effort” to kill police in Northern Ireland, a senior officer said.
A New IRA bomb discovered in a parked vehicle in Londonderry on Monday was to be used to attack a patrol, detectives said.
The device was operated using a command wire and was being stored for use somewhere else in the area.
Officers said it was improvised and contained commercial high explosives, which only required one adjustment to explode.
Assistant Chief Constable Mark Hamilton said: “All I can say is that there seems to be more of a concerted effort by dissident republicans.
“We have seen almost the re-emergence of the Continuity IRA in the Tyrone area, we also saw the attack in Craigavon, which we would attribute to CIRA.
“We have seen a regular tempo of activity in Derry/Londonderry from the New IRA.
“Only they can explain why they are doing it.”
The threat against members of the Police Service of Northern Ireland from republicans determined to undermine the peace process has been severe for a decade.
This was the eighth attack or attempted attack this year.
Others included the shooting dead of journalist Lyra McKee in Derry in April by a gunman targeting police, and the discovery of an explosive device under an officer’s car at a golf club in East Belfast.
Police launched a major search operation for bomb-making material in Creggan in Londonderry on Monday, which resulted in the discovery of the latest device.
Mr Hamilton said: “The use of this type of high-explosive in a community area has to be condemned.
“It is highly reckless, extremely dangerous and would have had devastating effects.”
The senior officer added: “The bomb would have killed or maimed anyone near it when it detonated.”
He admitted the tempo of dissident activity had increased.
“It is worrying for me as a police officer and I think it is worrying for communities and that is why now we need to stand very firmly together against this.”
Police were attacked with missiles by members of a crowd of 60 to 100 people as they carried out Monday’s searches targeting dissidents.
About 40 petrol bombs were thrown during the disorder.
The PSNI later said 15 families who were evacuated from their homes could return.
At least two young people engaged in the disorder sustained burn injuries during the violence, the PSNI said.
Mr Hamilton said: “By bringing a viable bomb into the community they have again proved that they have no regard for the lives of anyone living in Creggan.
“Once again they exploited some of the young people in the community to attack police and have brought disruption and misery to families.”
On Saturday a dissident republican mortar bomb was recovered in Strabane, Co Tyrone.
The mortar, which was positioned close to a family home, was aimed at the town’s police station.
Secretary of State Julian Smith commended the work of the PSNI. He spoke with Chief Constable Simon Byrne to discuss developments on Tuesday.
Mr Smith tweeted: “Earlier today I spoke to @ChiefConPSNI to offer my full support for the work he and his team are doing to keep people in Derry/Londonderry safe, despite coming under attack last night.”