Military grade explosives and several weapons which could have been used by dissident republicans to attack police have been recovered in Londonderry, the PSNI has said.
A senior officer said he believes children as young as eight were involved in the attacks.
Investigations are continuing but the "primary line of inquiry" has been described as dissident republican group the New IRA.
Two men and a woman were arrested under the Terrorism Act after the discovery of cash, handguns, grenades, ammunition and plastic explosives during three searches.
Northern Ireland Secretary Chris Heaton-Harris said his thoughts are with the officers who were injured.
"I would like to thank the PSNI for their work in keeping people in NI safe," he posted on social media site X, previously known as Twitter.
"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."
A number of items were located, resulting in a security alert and some residents being evacuated from their homes.
In a statement, police confirmed that detectives from the Terrorism Investigation Unit seized what are believed to be six improvised explosive devices, a quantity of ammunition and a machine pistol.
The items will be subject to rigorous forensic examination.
A police spokesperson said a large group of people gathered from 6pm and threw missiles at officers, including petrol bombs and masonry.
There were no reports of injuries on Friday night but the spokesperson described "extremely challenging circumstances" and "reckless and criminal behaviour" which "has to stop".
Earlier on Friday two senior police officers described the searches on Thursday as "exceptionally challenging".
Assistant Chief Constable Mark McEwan emphasised that the significance of the items seized "cannot be underestimated".
"These items are military grade and we believe the intention was to mount attacks in an attempt to kill police officers," he said.
"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," he 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 (attenuating energy projectiles) 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."
Policing Board chairwoman Deirdre Toner said: "The ferocity of violence and disorder directed against police officers during this search operation is condemned by the board, and must be condemned right across the community.
"Our thoughts are with all the officers injured."
Liam Kelly, chairman of the Police Federation, which represents rank-and-file officers, said they "displayed great courage and resilience and deserve great credit and the thanks of this entire community".
"Our officers did a thoroughly professional job. They undertook these searches to protect the immediate community and wider society and should be congratulated by all political parties and community groups," he 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."
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