An Israeli helicopter fired two missiles into Gaza City on Friday at what witnesses said was a refrigerator factory, hours after troops killed eight Palestinians during a massive offensive in northern Gaza. There were no reports of casualties. There was no immediate comment from the army, which has been pressing a wide-scale operation in northern Gaza after a rocket launched by Palestinians killed two Israelis in a border town. Thursday was Gaza's bloodiest day in four years of conflict, with 28 Palestinians and three Israelis killed. Israel has stepped up its air strikes since military forces thrust into northern Gaza on Tuesday.