Israel will halt its offensive in Gaza at 0000 GMT on Sunday but troops will remain in the enclave for the time being and will respond to Hamas fire, Prime Minister Ehud Olmert said on Saturday as he announced a unilateral ceasefire. "If our enemies decide to strike back and want to carry on then the Israeli army will consider itself free to respond with force." Olmert had earlier said that Israel had achieved all its goals in the massive three-week-long offensive -- the largest Israeli assault ever launched on the impoverished territory of 1.5 million Palestinians. More than 1,200 Palestinians have been killed since the war began on December 27, including more than 400 children. Ten Israeli soldiers and three civilians have been killed in the same period.