Mendez. With the onset of the Guatemalan army's first major anti-guerrilla offensive, the army and security forces carried out widespread extrajudicial killing, torture and forced disappearances. The repression was most intense in the southeastern region of the country, particularly in the department of Zacapa, under the command of Colonel Carlos Manuel Arana Osorio. In March 1966, thirty Guatemalan Party of Labour (PGT) associates were kidnapped, tortured, and killed by the security forces. This was one of the first major instances of forced disappearance in Latin American history. These 30 disappearances marked the beginning of a dramatic increase of state repression in 1966. When law students at the University of San Carlos used legal measures (such as habeas corpus petitions) to require the government to present the detainees at court, some of the students were "disappeared" in turn. In exchange for military support of his administration, President Mendez authorized the armed forces to use "any means necessary" to suppress the insurgency. No longer bound to the rule of law, the security forces resorted to terror to control the population and dismantle the civilian support base of the insurgency. Guatemalan government forces killed or "disappeared" thousands of civilians during the escalation of the counterinsurgency. The repression was most intense in the eastern regions where the MR-13 operated, and in Guatemala City where the PGT operated. In eastern Guatemala, government forces engaged in the massacre of civilians and destruction of peasant communities as a means of breaking up guerrilla bases. Some observers referred to the policy of the Guatemalan government as "White Terror" -a term previously used to describe similar periods of anti-communist mass killing in countries such as Taiwan and Spain- Observers estimate that as many as 15,000 Guatemalans were killed by the military and government-led death squads in three years of Mendez's presidency to eliminate fewer than 300 Marxist guerrillas. Amnesty International cited lower estimates of 3,000 to 8,000 peasants killed by the military during that time. Colonel Arana, who commanded the Guatemalan army, earned the nickname "Butcher of Zacapa" or "Jackal of the East." The victims included guerrilla sympathizers, labor union leaders, intellectuals, students, and people vaguely defined "enemies of the government." The government's use of "any means necessary" resulted in the opposition increasing its level of resistance to ensure its survival. The "White Terror" (which led to the destruction of the FAR's ladino peasant base in the eastern provinces)