Sixteen police officers have been injured during disorder which broke out in Londonderry after searches uncovered "military grade" weapons.
Police said two handguns, two military hand grenades, 50 rounds of ammunition and over a kilogram of plastic explosives were found in the Creggan area on Thursday.
Three people - two men and a woman - were arrested under the Terrorism Act.
Police believe the weapons would have been used in attacks on police officers and said their primary line of enquiry centres on the New IRA.
Assistant Chief Constable Mark McEwan said: "The significance of this recovery cannot be underestimated.
"These items are military grade, we believe the intention was to mount attacks in an attempt to kill police officers."
Disorder broke out following the searches and police officers were attacked with petrol bombs and heavy masonry.
Sixteen officers were hurt during the trouble - the Police Federation said four of them required hospital treatment.
Injuries they sustained included burns, head injuries and potential fractures.
Assistant Chief Constable Bobby Singleton said: "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."
ACC Singleton said officers had been granted authority to use baton rounds - but none were fired.
"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," he continued.
"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."
The searches were carried out in the Dove Gardens, SouthWay and Creevagh Heights areas as part of what police described as "an intelligence led proactive counter terrorist operation".
ACC McEwan said: “In the first search, in the area of Dove Gardens, over £2000 cash was seized.
"A further search then took place in the SouthWay area where we have recovered a handgun. A third search in the Creevagh Heights area where we recovered two military hand grenades, a further handgun, over 50 rounds of ammunition and over a kilogram of plastic explosives."
He continued: “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."
He said the investigation is ongoing and appealed to anyone with any information to come forward to police on 101 or through Crimestoppers.
Meanwhile a statement from the Policing Board condemned the violence, adding: "Our thoughts are with all the officers injured."
Liam Kelly from the Police Federation said: "I want to wish our injured officers well as they recover from their injuries.
"They did sterling work and showed great courage and resilience."
Posting on social media, Secretary of State Chris Heaton-Harris said: "I would like to thank the PSNI for their work in keeping people in NI safe.
"This is a reminder a small minority are still intent on causing harm to the community. My thoughts are with those officers injured in the course of their duties last night."
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