ROME, May 21 (AFP) - Italy was Friday facing up to the renewed threat of terrorism, after the extreme left Red Brigades, responsible for a campaign of deadly urban guerrilla warfare in the 1970s and 1980s, claimed responsibility for the murder of a government adviser. Massimo D'Antona was shot dead early Thursday as he left his home in Rome. The two gunmen fled. There were two claims of responsibility for the killing. One allegedly came from the "Armed Phalanx" -- a name used to claim responsibility for 1993 attacks against museums in Florence, Milan and Rome that were later blamed on the Mafia. The other was from the Red Brigades. That claim was contained in a 28-page document sent to Italian newspapers. The document refered to NATO, the war in Kosovo and sided with the Serbs in their fight against US "imperialism." It also criticized the policy of Prime Minister Massimo D'Alema's Left Democrats party, the main component in the left-leaning coalition government. It said traditional values of the left had been abandoned and labelled D'Antona one of the masterminds of the government's economic and social policies. The labour minister and mayor of Naples, Antonio Bassolino, for whom D'Antona worked as an adviser, said the government had "official confirmation of the terrorist origin of this attack." Officials said there was evidence of a carefully prepared assassination, noting that vans with tinted windows were found nearby and had probably been used for reconnaissance. D'Antona, 51, a former junior transport minister, trade unionist and labour law professor was not a public figure, working in the backroom for the government, and as such did not have any official protection. He was therefore an easy target. The Red Brigades were founded by Renato Curcio in 1973 amid an upsurge in support for the far left in the late 1960s and a series of bloody attacks blamed on the secret services and fascist groups. The Red Brigades are held responsible for hundreds of killings including the kidnapping and death of former prime minister and then leader of the Christian Democrats, Aldo Moro, in 1978. Curcio never committed any crimes himself but he also never gave up on his political beliefs and struggle. He was released after 17 years in prison in 1993. The claim of responsibility for D'Antona's killing was made in traditional Red Brigades style -- a call to media organisations revealing the whereabouts of documents containing the claims. Italy's political leaders were swift to responded. D'Alema said his government was "not afraid" of terrorism. "Terrorism wants to weaken and destabilize Italy at a particular moment" in international politics, he said, referring to the Kosovo crisis. He added that the violence "is to take Italy back into the past. "They have already been undone once; they will be beaten again; we will arrest them," he said. His comments were echoed by opposition leader Silvio Berlusconi. The Italian press reported Friday that the secret services had known about the terrorist revival but had underestimated the threat. Press reports cited earlier incidents including letter bombs to judges and a Communist deputy last year and a series of fire bomb attacks on US businesses including the fast food chain McDonald's.  