Police chiefs tonight warned of the unswerving lethal intent of dissident republicans following a thwarted letter bomb bid aimed at Northern Ireland Secretary Theresa Villiers.
The explosive package addressed to the Conservative MP, which was delivered to the seat of the power-sharing executive at Stormont Castle in Belfast, was the fourth such device intercepted prior to detonation in the region in less than a week.
The latest security alert forced First Minister Peter Robinson and other officials to evacuate the building.
The other bombs, two of which were discovered at Royal Mail sorting offices, were addressed to two senior police officers and an office of the Public Prosecution Service (PPS).
Sinn Fein tonight claimed a hoax device addressed to one of their councillors had also been found at a sorting office.
As Ms Villiers branded the "reckless" actions of the perpetrators, senior Police Service of Northern Ireland (PSNI) commanders warned a committee of MPs at Westminster that dissidents remained firmly wedded to violence.
PSNI Assistant Chief Constable Drew Harris told the Northern Ireland Affairs Committee: "There does not seem to be any diminution in their intent or any sense of them trying to find some route for dialogue with other parties or the Government.
"They seem entirely wedded to a route of violence."
Mr Harris expressed concern the extremists could get hold of more explosives and guns or make substantial amounts of money.
"We have concerns about upcoming anniversaries and whether they want to use those for their own purposes in getting publicity," he said.
Chief Constable Matt Baggott assured the committee members that intensive investigative efforts would go into finding the letter bombers.
The fourth device was discovered at Stormont Castle - where Mr Robinson and Deputy First Minister Martin McGuinness are based. As the Assembly is currently in recess over Halloween, Mr McGuinness was not in the property at the time.
Ms Villiers' base in Belfast is in nearby Stormont House.
However, today she was in London meeting former US diplomat Richard Haass to discuss progress on talks he is chairing with Northern Ireland politicians to address outstanding peace process issues.
After the meeting with the ex-White House envoy, she condemned the latest letter bomb attack.
"These attacks are totally unjustified, they will achieve nothing," she said.
"They are in defiance of the democratically expressed will of the people of Northern Ireland, indeed the whole of the island of Ireland who voted in such strong numbers for the current political settlement. It is a tragedy for Northern Ireland that there is a small minority that continue to seek to achieve their ends by terrorism and violence but they will not succeed because the vast majority of people in Northern Ireland have chosen the democratic route."
Ms Villiers added: " It might have had my name on it but the lives they were putting at risk are people who work in sorting offices, in post offices, civil servants - all those lives were put in jeopardy. I think that is disgraceful, I think it is reckless, that is why I condemn it."
She said the threat level continued to be severe and hailed the efforts of police on both sides of Irish border to thwart the dissidents.
"We will continue to bear down on that threat but there is not doubt that it is real, that there is continued attack planning by these dissident republicans," she said.
Earlier, Mr Robinson said those responsible for sending the devices had no regard for the lives of postal workers and staff working in offices.
"They will not further any aim or objective by their vile and callous deeds," he said.
"Northern Ireland will not be dragged back by terrorists who have nothing but misery to offer."
In the wake of today's alert, Mr McGuinness tweeted: "Letter bombs, attacks on places of worship, graves & orange halls are the offerings of bitter & twisted little minds & will further nothing."
Yesterday, a letter bomb was delivered to the offices of the PPS in Londonderry
Last Friday, similar devices were discovered at Royal Mail sorting offices addressed to Mr Baggott and Chief Inspector John Burrows, the police commander in Derry.
Police representatives today told the affairs committee that one suspected dissident republican is being arrested every week across Ireland, with a lmost 300 people having been detained by police in Northern Ireland alone since the start of 2010.
Mr Baggott said extra funding from the Treasury had helped the fight against the dissidents.
"The pressure at the moment is working but I would not want to give a long-term prognosis," he said.
The chief constable added: "They will exploit every opportunity to recruit young people and to use public disorder as a cover for attacks on police."
"What we can say with a very clear definitive statement is the investment (in resources to combat terrorism) is working."
He warned they could not allow terrorist groups to rebuild and pressed for enough money to boost the number of police officers.
Earlier Stormont's Justice Minister, David Ford, thanked staff in Royal Mail sorting offices for their vigilance when handling suspicious packages.
He visited the sorting office at Mallusk, near Belfast , where staff intercepted the viable explosive device addressed to Mr Baggott.
"There are delivery offices across Northern Ireland handling many thousands of letters and parcels every day," he said.
"Royal Mail has been very active in putting in place security measures to detect and deal with suspicious packages, which in turn helps to secure and protect our citizens.
"I was grateful for the opportunity to personally thank some of the staff involved in dealing with our mail and carrying out those security checks. There is an obvious threat to these staff when reckless people abuse the mail system and I commend them for their vigilance."
Mr Ford condemned the attempted attack on Ms Villiers.
"This is yet a further attempt to attack a public figure," he said. "Do those sending these devices really think their intended target will personally open the package? Their actions are to be condemned by all right-thinking people."
At Westminster, Mr Harris told MPs that the dissidents did not possess a major terrorist arsenal, a major batch of weapons or regular supply route.
He said some stolen shotguns and rifles have been recovered and some weapons not dealt with by decommissioning by paramilitaries.
Semtex explosives dating from 1982 have been seized as well as materiel from the Balkans conflict of the early 1990s, in common with organised crime groups across Europe, he added.
"We are always concerned about the amount of money that may be sloshing about these groups because anything is available to money and arms could be purchased is you have sufficient money," said Mr Harris.
In regard to the claimed hoax alert, Sinn Fein MLA Rosie McCorley said the party would not be intimidated from carrying on their work.
"Whoever is responsible for this needs to realise that any attempts at intimidation will just make us more determined to carry on that work," she said.