Security forces were bracing Tuesday night for a major escalation on the Gaza front out of concern that the deaths of 19 Palestinians, including the son of a top Hamas official, would spur the terror group to fire Kassam rockets into Israel. Hamas claimed responsibility for the killing of an Ecuadorian volunteer on a Gaza-belt kibbutz by a Palestinian sniper on Tuesday. The shooting took place in fields belonging to Kibbutz Ein Hashlosha near the Gaza border. Until now, while Hamas has assisted Islamic Jihad and the Popular Resistance Committees (PRC) in the production and delivery of Kassams, it has refrained from directly participating in their launching, preferring to operate via proxy. The concern within the defense establishment was that following the high number of Hamas casualties in Tuesday's operation, the terror group would decide to become directly involved in firing rockets. "If this happens, there will be a major increase in the number of rockets fired into Israel," a defense official explained. On Tuesday, 28 rockets pounded the western Negev and the city of Sderot. One scored a direct hit on a home, wounding five people, including a mother and her young daughter. Another rocket, a Grad-model Katyusha, hit an empty field in southern Ashkelon. Elite troops from the Golani Brigade's Egoz Unit, backed by tanks and Engineering Corps squads, swept into central Gaza early Tuesday morning in pursuit of Kassam rocket squads and terror infrastructure the IDF feared was being built up along the border fence. Nineteen Palestinians - including three civilians, according to hospital officials in Gaza - were killed in the ensuing gunbattles and air strikes. One was Hussam Zahar, 24, son of hard-line Hamas leader Mahmoud Zahar, who is viewed as the mastermind behind the violent Hamas takeover of the Gaza Strip in June. Zahar's eldest son, Khaled, was killed in 2003 when an F-16 dropped a bomb on his house in a failed attempt on Zahar's life. Palestinian Authority President Mahmoud Abbas condemned what he described as "the Israeli massacre in Gaza." According to the PA leader, Israel carried out barbaric actions that damage the peace process. "[We] cannot remain silent in light of these crimes," he said. Hamas declared three days of mourning throughout Gaza. Damascus-based Hamas leader Khaled Mashaal said that the IDF operation was the result of US President George W. Bush's visit to the Middle East. "This crime is the ugly fruit of Bush's visit to the region. He has incited the Zionists and has exerted pressure on the Palestinian side to become more hard-line against Palestinian dialogue," he said. Zahar accused Abbas of complicity in his son's death. "This is the hope of Abu Mazen and his colleagues, the collaborators with Israel and the spies of America," Zahar said, referring to Abbas by his nickname. Hamas, he vowed, would respond to Tuesday's raid "in the appropriate way. We will defend ourselves by all means." The foreign volunteer killed in a western Negev kibbutz by a sniper on Tuesday morning was identified as Carlos Andres Muscara Chavez, 20, from Quito, Ecuador. Chavez was working in a potato field in Kibbutz Ein Hashlosha, about 100 meters from the perimeter fence, when he was shot in the back. A Magen David Adom team summoned to the scene took the man, who was in serious condition, to the kibbutz infirmary, where he died of his wounds. Defense officials said that Tuesday's raid did not signify a change in policy and that no large-scale operation was expected in the immediate future. Officials acknowledged that raids like the one carried out in Gaza did not contribute to a positive atmosphere for talks with the PA, but said that the actions were "unfortunately necessary." "We are in a peace process, and we are also fighting terrorism, and both those things will continue in parallel," a senior government official said. An official in the Prime Minister's Office said that as much as Israel was willing "to be creative in negotiations, we will not compromise on security." The official also stressed that Tuesday's actions did not represent a new policy toward the Gaza Strip, but rather a continuation of activities over the last few weeks that have actively targeted terrorists. "These actions are designed to protect our people," the official said. "They are surgical incursions designed to deal with the terrorist infrastructure. The operations have been successful in taking out hardcore terrorists, and we believe that the combination of military, economic and political pressure in Gaza will bring about a change."