A rocket launcher and an accompanying warhead found in west Belfast is believed to be a Provisional IRA weapon that was not decommissioned.
Recovering it has saved lives, said the Police Service of Northern Ireland.
Police found the Russian-made RPG7 launcher in an unoccupied house in Hawthorn Street.
Large quantities of the weapons were brought into Northern Ireland by the Provisional IRA from Libya during the Gaddafi regime.
The new find was made by police investigating dissident republican activity.
The item has been taken away for examination.
Homes were evacuated following the discovery on Tuesday evening.
A PSNI spokesman said: "This is a significant seizure in that it shows the continuing intent of dissident terrorists to inflict death and serious injury.
"It also displays the callous disregard these small groups have for the lives of those in local communities, given where it was stored and its potential to injure or kill anyone in the vicinity of where it would have been fired.
"These weapons systems are clearly intended to kill and we should be in no doubt that the recovery of these items has saved lives."
West Belfast MP Sinn Fein's Paul Maskey said it was a "very worrying development".
"This community welcomes the fact this weapon is now off the streets," he said.
"[I have] no idea where it comes from, who had it. Obviously some form of dissident republicans have brought this into the area.
"Some people are stuck in the past and don't want to come out of it."
He said local people wanted the dissidents to come forward and explain why they have such weapons and why they are attacking the PSNI.
SDLP councillor Colin Keenan, who lives in Hawthorn Street, said local people were "shocked" that such weapons had been found in their area.
Mr Keenan said up to 10 houses had been evacuated and residents were given shelter in a nearby parish hall during the operation which began at about 20:00 GMT on Tuesday.
The residents were later allowed to return to their homes.
Earlier this month rocket launchers were intercepted in County Tipperary.
Irish police seized four rocket launchers and explosives believed to be en route to Northern Ireland.
Two men have already appeared before the Special Criminal Court in Dublin in connection with that find.