Gordon Brown visited the army base in Northern Ireland today where he held crisis talks with security chiefs and political leaders.
He was accompanied by Northern Ireland Secretary Shaun Woodward and police Chief Constable Sir Hugh Orde.
Sir Hugh, who had earlier called in undercover soldiers to carry out surveillance operations in a bid to thwart a heightening threat against his officers, ruled out putting troops back on the streets.
But the planning and execution of this double-murder after a series of failed attacks over the past two years will mean an immediate and urgent review of security measures.
There are an estimated 200-300 dissident republicans active in Northern Ireland and even though no more than a dozen may have been directly involved, detectives believe the two masked gunmen were clearly experienced in the use of high-powered weaponry.
Sir Hugh said: “This was an act by a small group of increasingly desperate people who are determined to drag 99 per cent of this community back to where they don’t want to go.”
The Real IRA South Antrim unit claimed responsibility in a phone call to the Sunday Tribune paper in Dublin.
In a statement, the paper said: “The caller said he made no apologies for targeting British soldiers while they continued to occupy Ireland and also said he made no apologies for targeting the pizza delivery men who, he said, were collaborating with the British by servicing them.”
The organisation is the same that killed 29 people - including a woman pregnant with twins - in the bombing of Omagh, Co Tyrone, in August 1998.
Prime Minister Gordon Brown and the Irish Taoiseach Brian Cowen insisted the killings would not disrupt the peace process.