Dissident Republicans are under suspicion after the discovery of a massive bomb in Newry – bigger than the device which killed 29 people in Omagh in 1998.
Viable devices and explosives were also discovered in North Belfast on Saturday in a massive security operation.
The first bomb alert in Newry uncovered a 600lb device in an abandoned van, twice the size of the Omagh bomb.
Two more alerts followed in Belfast as police reacted to a step-up in dissident Republican activity.
The Newry bomb was made safe by British Army experts in an operation that took over 36 hours. Local police chiefs said the device was larger than first feared and could have led to a major loss of life and destruction if detonated.
Police Service of Northern Ireland (PSNI) District Commander Chief Superintendent Alasdair Robinson said: “The device contained two blue barrels with 125kg of homemade explosives in each one, and a detonator - all the equipment which meant this device was ready to go.
“This was a very significant device. If this had exploded it would have caused devastation.
“To put it in perspective - anyone within 50 metres of this device would have been killed and anyone within 100 metres, seriously injured.”
Local Ulster Unionist parliament member Danny Kennedy claimed the device was designed to kill PSNI officers.
“The scale of the bomb suggests an attempt at a major attack by dissident republicans has been prevented,” said Kennedy.
“Clearly this was an attempt to lure a police patrol into that area, with potentially lethal consequences.
“These dissidents are dangerous and dedicated terrorists, who are determined to cause serious harm, injury and death to members of the security forces regardless of the consequences to local communities.”
Smaller devices were located and diffused in North Belfast where police also found arms and ammunition during searches.
North Belfast PSNI Chief Inspector Ian Campbell said: “Those responsible for this have shown callous disregard for members of the public.
“The operation resulted in the evacuation of up to 80 people, including families with young children and elderly residents, for several hours.
“The finger of suspicion points towards dissident republican terrorists and I appeal to anyone with information to come forward to police.”
District Chief Superintendent George Clarke told the Irish Times: “The actions of police have undoubtedly thwarted the attempts of criminals to inflict death, injury and misery on the community of north Belfast.
“Police are determined to protect communities from these threats.”
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