Tony Blair is having talks with Northern Ireland's party leaders amid heightening fears of a terrorist offensive by dissident republicans.
Hundreds of people in Londonderry had to be evacuated from their homes during the night after a failed mortar bomb attack on a military base. Army explosives experts also defused a bomb in the village of Claudy, near Derry.
Mr Blair is meeting Sinn Fein president Gerry Adams, Ulster Unionist leader David Trimble and Seamus Mallon, deputy leader of the nationalist SDLP.
The Prime Minister hopes to end the deadlocks over decommissioning, demilitarisation and policing arrangements. But the meeting in Downing Street has failed to raise expectations of an early breakthrough.
Fermanagh-south Tyrone Ulster Unionist MP Ken Maginnis declared: "I think there is very, very little room left for manoeuvre.
"It is ridiculous where we have those who want a return to violence and who are still active, and yet we have massive reductions in policing."
SDLP leader John Hume, MP for Foyle, whose constituency includes Derry, said he was appalled by the bombing.
"The people planting these bombs are the enemies of such a society. That will strengthen the people's desire to ensure we can move forward in a positive direction."
Sinn Fein's Martin McGuinness, the Mid Ulster MP who lives in Derry, rejected suggestions of Provisional IRA involvement in the attack.
He said: "I think we have to be concerned that there are still people within the nationalist and loyalist community who still believe that the way forward is to attack in a consistent basis in order to undermine and destroy all the work that the pro-Agreement parties have been involved in."