The military said aircraft and tanks hit eight Hamas positions in Gaza after its forces had been shot at and had "explosive devices" hurled at them along the border. More air strikes pounded Gaza as darkness fell in what the military described as a "wide-scale attack against Hamas."
Israeli media said Prime Minister Benjamin Netanyahu was holding discussions with cabinet colleagues and military chiefs about the escalation of hostilities during the long-running border protests on the Israel-Gaza frontier.
Hamas claimed three dead and the fourth, was a civilian, residents, and medics said. At least 120 Palestinians were wounded.
Palestinians have held the protests to demand the right to return to homes and villages from which they fled or were driven from during the conflict surrounding the creation of the modern state of Israel in 1948. But more recently some Gaza officials said the protests would end if Israel lifted an economic blockade of the Strip.
Israel says Hamas has been orchestrating the demonstrations to provide cover for militants' cross-border attacks. Hamas denies this.