The king of Spain told President Hugo Chavez to "shut up" after the fiery Venezuelan leader repeatedly called a former Spanish prime minister a "fascist," ending a regional leaders' summit in spectacular fashion. Chavez, who called US President George W. Bush the "devil" on the floor of the United Nations last year, triggered Saturday's exchange with harsh words for former Spanish Prime Minister Jose Maria Aznar, who has in the past criticized Chavez. Aznar, who was a close ally of Bush as prime minister, "is a fascist," Chavez said in a speech at the Ibero-American summit in Santiago, Chile. "Fascists are not human. A snake is more human," Chavez said. Spain's current socialist prime minister, Jose Luis Rodriguez Zapatero, responded during his own allotted time by urging Chavez to be more diplomatic in his words and respect other leaders. "Former President Aznar was democratically elected by the Spanish people and was a legitimate representative of the Spanish people," he said, eliciting applause from the gathered heads of state. "President Hugo Chavez, I think there is an essential principle to dialogue, and that is, to respect and be respected, we should be careful not to fall into insults," Zapatero said, noting the ideological differences he himself had with his conservative predecessor. Chavez repeatedly tried to interrupt, but his microphone was off. Spanish King Juan Carlos, seated next to Zapatero, angrily turned to Chavez and said, "Why don't you shut up?" The Venezuelan leader did not immediately respond, but later used time ceded to him by his close ally Nicaraguan President Daniel Ortega to answer Zapatero's speech. "I do not offend by telling the truth," he said. "The Venezuelan government reserves the right to respond to any aggression, anywhere, in any space and in any tone." In subsequent comments reported on the Web site of Spanish newspaper El Mundo, Chavez said: "I speak the truth to kings, to imperialists, to Bush." In a speech to 18 presidents gathered in Santiago for the annual Ibero-American Summit, Chavez claimed that Aznar in 2000 asked him to distance Venezuela from Cuba and join "the club." Chavez said he'd refused. Chavez - a close ally of Cuban leader Fidel Castro - says he is steering oil-rich Venezuela toward what he calls "21st-century socialism," and has exchanged repeated barbs with officials from the United States and other countries opposed to his government. At home, he is facing demonstrations by tens of thousands of university students opposed to proposed constitutional reforms that would expand his power. Chavez, however, still maintains broad popular support. Saturday's exchange between Chavez, Zapatero, and Spain's king overshadowed a three-day summit that ended with leaders pledging to fight poverty and increase regional cooperation. Heads of state there signed a landmark accord that will allow nearly 6 million migrant workers in Latin America, Spain and Portugal to transfer social security benefits between their nations. The leaders also vowed to fight "all forms of terrorism" and called on the US to end its economic embargo against Cuba. After the summit, Chavez joined the presidents of Bolivia and Nicaragua, along with Cuba's vice president, at a parallel "People's Summit" organized by leftist groups. Cuban Vice President Carlos Lage handed Chavez a cell phone as the Venezuelan leader addressed the crowd, saying that Fidel Castro was on the line. Chavez listened briefly and told his audience that Castro was "paying tribute to international and Chilean combatants who fell fighting tyranny."