GAZA (Reuters) - Israel destroyed Hamas's main Gaza security complex in an air strike on Sunday and prepared for a possible invasion of the territory after killing nearly 290 terrorists in the opening rounds of a powerful offensive. The campaign that began on Saturday was a response to almost daily rocket and mortar fire that intensified after Hamas ended a six-month ceasefire a week ago. "Israel will continue (the campaign) until we have a new security environment in the south, when the population there will no longer live in terror and in fear of constant rocket barrages" said Mark Regev, a spokesman for Olmert.