Police have seized explosives, two hand grenades and two handguns during searches in Derry.
Sixteen police officers were hurt during rioting linked to the operation on Thursday evening.
Three people - two men and a woman - were arrested under terrorism legislation.
Police say they believe the material is linked to the so-called New IRA, and the intention was to use them to attack their officers.
In the first of three searches, £2,000 in cash was found at Dove Gardens, while during a subsequent search at Southway a handgun was found.
A further handgun, two military hand grenades, a kilogram of plastic explosives and 50 rounds of ammunition were found in a search at Creevagh Heights.
Assistant Chief Constable Mark McEwan said the significance of the items could not be underestimated.
"These items are military grade and we believe the intention was to mount attacks in an attempt to kill police officers.
"They were being stored in a residential area close to a children's play area and any attack that would have been mounted would have taken place within our communities."
The police said the officers injured during the rioting had been pelted with masonry and petrol bombs.
They sustained burns, head injuries and fractures.
Police thanked community leaders who had helped to try and calm the situation as homes were evacuated to deal with the situation.
"I want to pay tribute to our officers and staff against the backdrop of a severe terrorist threat against them, within the last year, with the attempted murder of DCI John Caldwell, most recently the data loss and the events of the last week, they have continued to deliver a first-class policing service," Mr McEwan said.
