South American leaders gathered in Rio Janeiro for a two-day summit on Thursday (January 18) hoping to strengthen the Mercosur trade bloc but facing pressure from the socialist crusade of Venezuela's Hugo Chavez. A heavy security operation was mounted to protect the presidents of Venezuela, Argentina, Uruguay, Paraguay and Brazil following a wave of gang violence in the city. Troops in armoured cars guarded highways, a warship patrolled Rio's scenic bay, and soldiers set up machine-gun posts overlooking the city's shantytowns, many of which are controlled by drug gangs. The Mercosur members -- Brazil, Venezuela, Argentina, Uruguay, and Paraguay -- are joined by the leaders of Bolivia, Ecuador, Chile and other countries at a luxury hotel on the famed Copacabana seafront. Venezuelan president Hugo Chavez, who last week announced plans to nationalize key industries, caused a stir wherever he went. He said that unity among South American nations was at the top of his agenda. "Integration brothers, the conscience that we are one nation, Rio de Janeiro, Caracas, Lima, Buenos Aires, we are of the same nation. South America is a great nation and we have to advance for the unity of our republic (South America)," he said. However, some of his regional counterparts, who represent more moderate shades of a left-wing surge in Latin America, are uneasy with Chavez's avowed crusade to spread "Socialism for the 21st Century" backed by oil money and anti-U.S. taunts. Following Chavez's arrival at the Copacabana Palace hotel, came various other South American leaders like Colombia's Alvaro Uribe, Chile's Michele Bachelet and Ecuador's Rafael Correa. The leaders then met in closed meeting where they began to discuss, among others, the bloc's possible reform. Chavez and Brazilian President Luiz Inacio Lula da Silva, who are friends but also rivals in their ambitions to lead the region, lunched together before the summit's formal opening. The bloc, which was created in 1991 and represents some 250 million people, is split by internal trade disputes and has made little progress toward regional integration or becoming an effective counterbalance to U.S. and European trade dominance.