Addressing mayors of southern border towns hit by the surprise attack by Islamist militants Hamas that began Saturday, Israeli Prime Minister Benyamin Netanyahu said what Israel will do now will "change the Middle East."
Meanwhile, Israeli Defense Minister Yoav Gallant said that Israel will impose a complete siege on Gaza, the territory controlled by Hamas.
"We are putting a complete siege on Gaza, there will be no electricity, no food, no water, no fuel, everything will be shut down. We are acting accordingly," said the Israeli minister, Gallant.
The Israeli army said it had called up 300,000 reservists. This and the siege of Gaza are taken as signs that Israel is planning a ground attack to defeat Hamas.
Israel has also sent tanks and soldiers to the border with Lebanon. Israeli officials said the country's military, backed by helicopter gunships, had killed a number of gunmen who had crossed into Israel from Lebanon, raising fears that the fighting could spread wider in the region.
Israel officially declared a state of war on Sunday, warning of more fighting and a possible ground attack on Gaza, an action that has caused many casualties in the past.
Palestinian Prime Minister Mohammad Shtayyeh said Monday that Palestinians have the right to defend themselves from Israeli aggression and occupation.
"These events and their consequences are the result of the Israeli government's policy of using the worst methods of aggression, murder, land confiscation, attacks on holy sites and terrorism. Aggression and security measures cannot produce peace for Israel or tranquility for Israelis," says Mr. Shtayyeh.
Hamas continued to attack Israel with rockets, sounding air raid sirens from Jerusalem to Tel Aviv.
Israel responded by striking more than 1,000 targets in Gaza, and tanks and drones guarded the damaged border fence with Gaza to prevent further militant gains into Israeli territory.
Hamas is deeply rooted in Gaza and has ruled the territory since the expulsion of forces loyal to the internationally recognized Palestinian Authority in 2007. Its rule has gone unchallenged through a 16-year Israeli and Egyptian blockade and four previous wars with Israel.
After breaching Israeli roadblocks with explosive devices at dawn on Saturday, Hamas gunmen went on the offensive for hours, killing civilians and kidnapping people in cities, along highways and at a music festival attended by thousands in the desert. . Palestinian militants have also fired about 4,400 rockets into Israel, according to the military.
The Israeli military estimated that 1,000 Hamas fighters took part in Saturday's initial intervention. The high number pointed to the extent of planning by the militant group, which has said it launched the attack in response to the growing suffering of Palestinians under Israeli occupation of the West Bank, the blockade of Gaza, discriminatory policies in annexed east Jerusalem and tensions over a holy place for Muslims and Jews in Jerusalem.
Palestinians want a state of their own in all three territories captured by Israel in the 1967 war, but the last serious peace talks broke down more than a decade ago and Israel's far-right government opposes Palestinian statehood.