Groups such as the loyalist UDA and UFF, as well as the IRA, are continuing to train and have access to "significant quantities" of arms and explosives, Mr Flanagan said.

He was speaking in a lecture to the Royal United Services Institute in London.

Threat continues

Mr Flanagan said: "All of the existing paramilitaries holding to their definition of a cessation of a violence have to be said to continue to pose a threat."

The greatest threat to peace is from splinter groups

But he stressed that the most immediate threat continued to come from splinter groups - such as the INLA, Continuity IRA and the 32 Counties Sovereignty Committee - which oppose the peace process and have not called ceasefires.

Such groups had been responsible for a whole series of recent attacks in the province, he said.

Praise for Garda

During his speech, Mr Flanagan praised the Irish Garda for their success in countering terrorist groups in the Irish Republic - most recently at the weekend when they intercepted two cars heading for the border carrying 900lb of explosives.

He also welcomed the decision to establish an independent commission under the chairmanship of former Hong Kong governor Chris Patten to review the future of policing in Northern Ireland in the light of the peace settlement.