The "Real IRA" is being blamed for a series of bomb alerts in Belfast, Co Armagh and at the international airport at Aldergrove, Co Antrim.
Hoax devices were left on a bus in central Belfast and at CastleCourt shopping centre near City Hall, causing traffic chaos and clearing the streets of the business district of workers and shoppers.
There was a series of alerts across north Belfast and there was also disruption in Lurgan and at Aldergrove, although no flights were affected. All the incidents were later declared hoaxes.
The alerts appeared to be co-ordinated and organised by the "Real IRA" in response to the statement by prisoners in Portlaoise prison at the weekend which called for the organisation to be disbanded.
The group has associated itself with a bomb incident at Castlederg police station in Co Tyrone at the weekend.
Security sources maintain they take the "Real IRA" threat seriously despite prisoners' withdrawal of support from the organisation.
The organisation, formed in 1997 and which bombed Omagh in 1998, is said to be torn by internal dissent and poor communications between the leadership, prisoners and activists.
The SDLP leader condemned yesterday's hoaxes.
"Disorder of this kind is completely wrong and can have no place in our society.
"I want to see an Ireland where there are no paramilitaries whatsoever and where all the people can live in peace and without fear," Mr Mark Durkan said.
Echoing the call by Mr Tony Blair for an end to paramilitarism in his Belfast speech last Thursday, Mr Durkan added: "The truth is that paramilitary actions such as these are only deepening divisions, increasing bitterness and holding us all back." His condemnation came as the Northern Secretary and the Minister for Foreign Affairs prepared to meet later today .
Dr John Reid will meet Mr Cowen at Hillsborough for talks - their first since suspension of the Executive and Assembly last week. It will signal a fresh round of talks between the parties and the two governments in the coming weeks.
In the US, Sinn Féin's Mr Martin McGuinness is scheduled to hold talks with President Bush's special adviser on the North, Mr Richard Haass.
Mr McGuinness said yesterday his party was "in the business" of "resolving the issue of all armed groups" in Northern Ireland.
He said that Mr Tony Blair's speech last week was a tacit admission that the Belfast Agreement had not been fully implemented by the British government. The former education minister also called for all-party talks to kick-start the political process.
"I will brief Ambassador Haass on the current situation and outline to him our view that the British government should reinstate the institutions, that the two governments should call all-party talks and the two governments should produce their plan and implement the agreement," he said.
The "Real IRA" in the north-west warned yesterday that it was planning to step up its attacks on police and army bases.
The statement, issued 48 hours after the "Real IRA" prisoners in Portlaoise Prison called for their leadership to stand down, was accompanied by a recognised code-word.
The threat of further violence also followed Sunday's bomb attack on Castlederg PSNI station in Co Tyrone, which was admitted by the "Real IRA". In that attack the bomb failed to explode, but a senior police officer said that had the device exploded, there could have been widespread casualties.
The "Real IRA" statement said: "We warn all civilians to stay away from military installations and from crown forces personnel. A number of recent attacks had to be aborted due to the presence of civilians. Anyone entering military installations does so at their own risk."