A dissident republican group opposed to Northern Ireland's power-sharing government said Sunday it shot dead two British soldiers at an army base, the first such killing in 12 years. The victims were collecting the pizza at the Massereene base near the town of Antrim, 25 km northwest of Belfast, when gunmen pulled up in a vehicle and opened fire. There was one burst of gunfire then the attackers walked forward and shot the victims as they lay on the ground, Irish public broadcaster RTE reported. Suzanne Breen, a reporter with the Irish Sunday Tribune newspaper, said she received a telephone call Sunday evening from a man who made “no apology” for the attack. “A man who said he was a representative of the South Antrim Brigade of the Real IRA claimed responsibility for the attack,” Breen told BBC television. “He said that he made no apology for attacking British soldiers in Massereene army base nor the men who were delivering pizza to them, who he called collaborators with the British rule in Ireland. The two soldiers who were killed were in their early 20s and were due to fly out to Afghanistan. British and Irish political leaders condemned the Saturday night attack and said it must not derail the peace process. The Irish nationalist party Sinn Fein said Republicans had a duty to oppose what it called a “wrong and counterproductive” act. “They want to destroy the progress of recent times and to plunge Ireland back into conflict,” Sinn Fein President Gerry Adams said in a statement. It was one of the worst attacks in Northern Ireland since the 1998 peace deal was signed to end decades of political and sectarian strife. British Prime Minister Gordon Brown called it an “evil and cowardly” action. “I assure you that we will bring these murderers to justice. No murder will be able to derail a peace process that has the support of the vast majority of the people of northern Ireland and we will step our efforts to make the peace process one that lasts and endures,” he said in a broadcast statement. Irish Prime Minister Brian Cowen said, “A tiny group of evil people cannot and will not undermine the will of the people... to live in peace together.” Four people, including two pizza delivery men, were also wounded in the attack, RTE reported.