"My instructions are to prepare for the possibility of significantly widening the ground operation, and the military is preparing accordingly," Israeli Prime Minister Benjamin Netanyahu told reporters after convening a meeting of the security cabinet to discuss the Gaza situation.
Netanyahu said the military was targeting the Hamas tunnel network, which it could not do "only from the air".
Security sources in Israel said that the need to neutralise the subterranean threat was one of the reasons behind the launch of the ground operation.
Netanyahu also emphasised that Israel launched the ground incursion only after Hamas rejected ceasefire proposals.
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"The operation came after Israel agreed to the Egyptian and UN proposed ceasefires. In both cases Hamas continued to shoot, and in light of that we chose to begin the operation after exhausting all other options, understanding that without expanding the operation, the price we will pay will be higher," he said.
Israeli Defence Minister Moshe Ya'alon also spoke at the meeting, saying "we will not compromise on Israel's security and will not accept rocket fire on the south".
"Hamas has already begun to pay a heavy price for its actions, and will pay even more dearly until rocket fire stops. Whoever attempts to disrupt our life will regret it," Ya'alon said.
Israeli forces backed by artillery and airstrikes launched the ground offensive last night with the army intending to strike a "significant blow to Hamas' terror infrastructure".
"Following 10 days of Hamas attacks by land, air and sea, and after repeated rejections of offers to de-escalate the situation, the IDF has initiated a ground operation within the Gaza Strip," a statement from the Israeli army said.
The Israeli Defense Forces (IDF) said the goal was to "establish a reality in which Israeli residents can live in safety and security without continuous indiscriminate terror.