The surprise assault by Hamas against Israel was a meticulously planned offensive that the Palestinian militant group is capable of keeping up, with a risk of even greater escalation, analysts say.

Hamas can count on a deep arsenal of rockets to use against Israel but key questions include how much support it has received from Iran, which has expressed its backing for the offensive, and whether Hezbollah will enter the fray.

Iran on Monday rejected as unfounded allegations it had a role in the massive assault on Israel by the Palestinian Islamist group Hamas.

"The accusations linked to an Iranian role... are based on political reasons," foreign ministry spokesman Nasser Kanani told reporters, adding that Palestinians had "the necessary capacity and will to defend their nation and recover their rights" without any help from Tehran.

Israel's defense minister ordered Monday a "complete siege" on the Gaza Strip following an unprecedented incursion into Israel by Hamas fighters.

Israel formally declared war on Sunday and gave the green light for "significant military steps" to retaliate against Hamas for Saturday's surprise attack. More than 1,100 people have been killed and thousands wounded on both sides.

Defense Secretary Lloyd Austin said he has ordered the Ford carrier strike group to sail to the Eastern Mediterranean to be ready to assist Israel after the attack by Hamas that has left more than 1,000 dead on both sides. Americans were reported to be among those killed and missing.

The USS Gerald R. Ford, the Navy's newest and most advanced aircraft carrier, and its approximately 5,000 sailors and deck of warplanes will be accompanied by cruisers and destroyers in a show of force that is meant to be ready to respond to anything, from possibly interdicting additional weapons from reaching Hamas and conducting surveillance.

The U.N. Security Council has held an emergency meeting behind closed doors, with the United States demanding all 15 members strongly condemn "these heinous terrorist attacks committed by Hamas," but they took no immediate action.

U.S. deputy ambassador Robert Wood said afterward that "a good number of countries" did condemn the Hamas attack but not all council members. He told reporters they could probably figure out one of them.

Israel's military scoured the country's south for Hamas fighters and guarded breaches in its border fence with tanks on Monday, as it pounded the Gaza Strip from the air and mustered for a campaign its prime minister said would destroy "the military and governing capabilities" of the militant group.

More than two days after Hamas launched its unprecedented incursion from Gaza, the military said the fighting had largely died down for now. The attack caught Israel's vaunted military and intelligence apparatus completely off guard, bringing heavy battles to its streets for the first time in decades.

The conflict between Israel and Hamas militants is making a global impact with Britain, Canada, France and Germany among nations stepping up security around potential Jewish targets as pro-Palestinian protests break out in the Middle East.

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Iranian President Ebrahim Raisi said on Sunday that Iran supports the Palestinians' right to self-defense and warned Israel must be held accountable for endangering the region, a day after Hamas attacked Israel.

Palestinian militants from the Iran-backed Islamist group Hamas, which controls the Gaza strip, penetrated Israel at dawn on Saturday under the cover of a massive rocket barrage.

Israel's army said Sunday it aims to evacuate all Israelis living close to the Gaza Strip within 24 hours as it deployed tens of thousands of soldiers to fight Palestinian militants who had infiltrated into Israel.

"Our mission for the upcoming 24 hours is to evacuate all residents living around Gaza," military spokesman Daniel Hagari told reporters, adding that fighting was still on to "rescue hostages" held by militants in Israel.

Two Israeli tourists and one Egyptian were killed Sunday by a policeman in Egypt, local media and Israeli authorities said, as war rages for a second day between Israel and Hamas.