Northern Ireland police have discovered four live mortar bombs during a thwarted attack by dissident republicans in Londonderry.
They were discovered in the back of a van which had a section of its roof cut back as part of plans to bomb a police station in the city, a senior officer confirmed.
Three men, all in their 30s, were arrested - two at the scene. One was detained in searches afterwards.
It is understood one of the men had been on a motorcycle following the van when police intercepted it near the city centre on Sunday night,.
More than 100 homes had to be evacuated in the Brandywell area.
Police rammed the van and a motorcycle was also intercepted during what appears to have been a carefully planned operation.
Pat Ramsey, an SDLP member of the Assembly who lives in Derry, said the interception of the bombs was down to swift police action.
He said: "The fact that the van's roof had been cut back shows that there was real intent to use these devices to cause serious injury or death.
"I am dismayed that dissident republicans continue to pursue activity which shows a ruthless disregard for human life. Any threat to those people who work to uphold the rule of law is totally abhorrent.
"This special year for Derry cannot be overshadowed by the reckless efforts of a delusional minority.
"People here deserve to live in a society free from violence and the threat of violence."
Dozens of homes evacuated after the white van was brought to a halt shortly after 8pm as it headed towards the city from the border.
A wide area was sealed off and as homes were evacuated with residents being moved to Brooke Park Leisure Centre and Celtic Park GAA ground.
Police commander Chief Superintendent Stephen Cargan said he believed terrorists were just about to launch the attack, probably on one of the Police Service of Northern Ireland stations in Derry, this year's UK City of Culture.
East Londonderry MP Gregory Campbell claimed: "We were 10 minutes away from a disaster. That is how close we were to a really bad night in Londonderry.
"The mortars were ready to be fired. There could have been dozens of people killed."
Security chiefs were obviously working on good intelligence and had mounted a surveillance operation to foil the attack, he said.
Raymond McCartney, a Sinn Fein member of the Northern Ireland Assembly, said: "The overwhelming majority of people in Derry will be relieved these weapons are off the streets. There is no place for these people who call themselves dissident republicans in the 21st century."
Mr Cargan said the van had been stopped in Letterkenny Road and four live mortar bombs found.
He said: "They were destined for a police station in the Derry. It was a reckless attack. They were prepared to drive through a built-up area of the city to carry out this attack and cause mass fatalities.
"These devices were primed. They are crude home-made devices and there is no way people who made these bombs would be certain they would have hit their target. There would have been mass murder of police, and serious damage to property.
"Good police work prevented this. If these devices had not been intercepted we would have been looking at a completely different picture. It is a very worrying development. Dissident republicans want to take us back to a place no-one wants to go to."
One eyewitness said she saw at least two people being arrested.
She said: “I saw the police vehicles racing along the Foyle Road and I went over to see what was going on.
“I could see a motorbike lying on its side and a white van.
“There was one fella being held across a car and then they put him into a police car and took him away.
“They then put another person into a car and I thought, although I couldn't be sure, that this was a girl and they left as well.”
Police then sealed off a wide area at the junction of Foyle Road and the Letterkenny Road.
Late last night officers at the scene would only confirm that a number of people had been arrested and that Army explosives experts had been called in to assess what was in the van.
However, they said there was some concern at the possible size of the device and there were reports that the cordon was going to be extended to take in other nearby streets.
Speaking at the scene, SDLP MLA Pat Ramsey said his first reaction was gratitude that the suspected device had been intercepted.
He said: “Whatever is in this van it does appear that there was going to be an attack on the city tonight so I am glad that it has been caught.
“However, there are quite a number of people who have had to leave their homes and I know this has caused great anxiety and distress to many of the elderly people who live in this area.”
People stayed out of their homes last night and it remained unclear how long it would take before the area could be declared safe.