Israel threatened on Sunday to launch a major offensive against the Hamas-ruled Gaza Strip as violence simmered around the impoverished territory days after the end of a truce with the Islamists. The two frontrunners in the race to become prime minister after a snap election in February both vowed to topple Hamas, which has run Gaza since violently seizing power there in June 2007. "Israel must topple the Hamas rule in Gaza and a government under my command will do just that," Foreign Minister Tzipi Livni, who leads the Kadima party that heads the government coalition, was quoted as saying by Israeli media.