Stephen Carroll was shot dead in Craigavon
A return to terrorism in Northern Ireland will never be tolerated, a forum of British and Irish politicians has said.
The British-Irish Parliamentary Assembly adopted a motion condemning the dissident republican murders of two soldiers and a policeman.
Bipa co-chairman Niall Blaney said there was unity against violence across the political spectrum.
"Peace is paramount and nothing will be allowed to derail that process."
The police are continuing to investigate the murders of soldiers Mark Quinsey and Patrick Azimkar in Antrim and PSNI officer Stephen Carroll in Craigavon earlier this month.
The motion said Irish and British politicians were appalled by the deaths and "unreservedly condemn the recent murderous attacks, intended to undermine the peace settlement endorsed in referenda by the people of the island, north and south".
It was seconded by former Northern Ireland Secretary of State, Peter Hain, who earlier told the BBC that the dissident groups had to be thwarted.
"It wasn't a surprise to me that those killings happened. Hugh Orde had said at some point it was likely the dissident groups would bring success in their own hideous terms," he said.
"But things have moved on so far in Northern Ireland that they are not going to be taken back to the terrible Troubles of the past by those killings."
Security was stepped up ahead of the conference which is taking place in the Solís Lough Eske Castle Hotel, near Donegal town.
Later, delegates will hear from Lord Eames and Dennis Bradley on their recent proposals for victims of the Troubles.
The British-Irish Parliamentary Assembly was formerly the British-Irish Inter-Parliamentary Body. It was formally established in 1990 as a link between Westminster and Dublin.
It has 25 British and 25 Irish members with membership extended recently to include representatives from the Northern Ireland Assembly, the Welsh Assembly, the Scottish Parliament and the Isle of Man and the Channel Islands.