Several items seized during searches in Derry would have been used with the intention of attacking officers, the PSNI has said.
Investigations are ongoing but the “primary line of inquiry” is on the New IRA, a senior officer said.
Trouble broke out on Thursday night as detectives from the terrorism unit carried out three searches in the Creggan area of the city as part of an ongoing investigation.
Petrol bombs, rocks, masonry, steel poles and traffic cones were thrown, with sixteen injuries to officers reported.
The PSNI said officers had to maintain a presence while searches were carried out and described the circumstances as “exceptionally challenging”.
Among the items seized from the three locations searched were two hand grenades, a handgun, more than 50 rounds of ammunition and in excess of a kilogram of plastic explosives.
More than £2,000 (€2,300) in cash was seized in the area of Dove Gardens while a handgun was found in the search in the South Way area.
During a third search in the Creevagh Heights area, two military hand grenades, another handgun, over 50 rounds of ammunition and over a kilogram of plastic explosives were found.
Two men and a woman have been arrested under the Terrorism Act and remain in custody.
Assistant Chief Constable Mark McEwan said: “The significance of this recovery cannot be underestimated. These items are military grade and we believe the intention was to mount attacks in an attempt to kill police officers.
“Whilst the investigation is ongoing, and while we keep an open mind, the primary line of inquiry centres on the New IRA.
“Not only was the intention here to kill and maim, but there is a total disregard for the wider community.
“These items were being stored in a residential area in close proximity to a children’s play area and any attack that would have been mounted would have taken place within our communities.
“This is clearly extremely worrying for the wider community and for officers and staff, but be assured that the success of this recovery demonstrates our dedication to pursuing these groups, the professionalism of our teams and our dogged determination to bring these people before the courts.”
Assistant Chief Constable Bobby Singleton said the injuries to officers included burns, head injuries and potential fractures, and praised their courage and “restraint”.
“Yesterday was an exceptionally warm day which combined with the time of day drew large numbers of youths to the area,” Mr Singleton said.
“Regrettably, the situation quickly escalated, with officers and their vehicles coming under sustained violent attack with heavy masonry and petrol bombs.
“Because of the material found, police had to maintain a presence over an extended period for our security and public safety.
“These were extremely difficult conditions for our officers, many of whom were in full personal protective equipment and at this time we have 16 reported injuries to our officers from our tactical support groups and our local policing teams.
“Officers who, today, will not be able to serve the community. The injuries sustained include burns, head injuries and potential fractures. We are really proud of our officers who demonstrated not only real courage and professionalism but also amazing restraint in the face of this violence.
“Authorisation had been given for deployment and use of our AEP systems but no rounds were fired. I would also like to take this opportunity to thank our partners, community leaders and families in Creggan for their support, patience and understanding.
“A number of families had to be evacuated from their homes to make safe these dangerous munitions.”
