Political leaders in Britain and Northern Ireland condemned Sunday the murder of two British soldiers at an army barracks, as the police investigation into the shooting began, according to dpa. British Prime Minister Gordon Brown condemned as "evil" the attack on Saturday night, which took place as the army base north of Belfast took delivery of takeaway pizzas. Four others, including the two pizza delivery men, were injured. One of the injured is said to be in a critical state. It is the first lethal attack on British forces in Northern Ireland in 12 years. Northern Ireland's First Minister Peter Robinson has postponed a planned trip to the United States to respond to the tragedy. Brown, speaking in London, said: "No murderer will be able to derail a peace process that has the support of the great majority of Northern Ireland." "I think the whole country is shocked and outraged at the evil and cowardly attacks on soldiers serving their country." "We will do everything in our power to make sure that Northern Ireland is safe and secure and I assure you we will bring these murderers to justice," Brown added. No group had yet claimed the attack but it is being blamed on dissident republicans. Investigating officer of the Northern Ireland Police Service, Detective Superintendent Derek Williamson, said that at least two gunmen opened fire on the group of soldiers at the barracks, as well as on the two pizza delivery men, local daily the Belfast Telegraph reported. WIlliamson said that as part of the police investigations, officers were questioning if the delivery men had been deliberately targeted in the attack. He said Dominos Pizza in the town had received two separate delivery orders from the base at around 9.20pm. The orders were sent out separately and the two delivery men arrived one after the other. It was at this point when gunmen opened fire from a car. The governments in Northern Ireland, London and Dublin have all sharply condemned the shooting. Sinn Fein president Gerry Adams, whose party led the militant Republican movement into political negotiations in the 1990s, called it an "attack on the peace process." "Those responsible have no support, no strategy to achieve a United Ireland. Their intention is to bring British soldiers back onto the streets," he said. Ian Paisley Junior, a Democratic Unionist member of the Northern Ireland Assembly, warned: "This could be a defining moment in the history of Northern Ireland." "For the last 10 years, people believed things like this happened in foreign countries, places like Basra. Unfortunately it has returned to our doorstep," he said. The president of the European Parliament, Hans-Gert Poettering, called it a a "dispicable and murderous attack ... on the democratic institutions of Northern Ireland." Robinson, who became first minister under the province's power- sharing government, called the attack "a terrible reminder of the past." More than 3,000 people were killed in the conflict between nationalist Catholics and unionist Protestants in Northern Ireland since the 1960s, until the Good Friday Agreement was signed in 1998. The police chief of Northern Ireland, Sir Hugh Orde, had warned just days before the attack that there was a renewed threat to peace from dissident republicans.