The prime minister has warned that the government will take a tough line in assessing whether paramilitary groups are observing their ceasefires.

Tony Blair's comments came before a statement by the Northern Ireland secretary, Dr John Reid, in which he said that the government would use the "full force of the law" against terror groups.

Speaking in the Commons, the prime minister said ceasefire judgements should become "increasingly rigorous".

"Now, more than four years after the agreement was signed, it is increasingly urgent that it should be clear that paramilitary organisations are not engaged in any preparations for terrorism and that they should be stood down altogether as soon as possible," he told MPs.

Writing in today's Telegraph, Ulster Unionist leader David Trimble says: "The government needs to save Sinn Fein from itself, by compelling it to face political reality."