Israeli troops prepared on Sunday for a ground assault on the Hamas-controlled Gaza Strip as the country hit back for an unprecedented assault on its territory, and Iran warned of "far-reaching consequences" if Israel's bombardment was not stopped.

Israel has vowed to annihilate the militant group Hamas in retaliation for a rampage by its fighters in Israeli towns eight days ago in which its militants shot men, women and children and seized hostages in the worst attack on civilians in the country's history.

Some 1,300 people were killed in the unexpected onslaught, which shook the country with horrifying mobile phone video footage and reports from medical and emergency services of atrocities in the overrun towns and kibbutzes.

Israel responded by subjecting Gaza to the most intense bombardment it has ever seen, putting the small enclave, home to 2.3 million Palestinians, under total siege and destroying much of its infrastructure.

The expected ground assault had not begun by the early hours of Sunday.

U.S. Secretary of State Antony Blinken began a meeting with Saudi Crown Prince Mohammed bin Salman in Riyadh soon after 7:30 a.m. (0430 GMT), a U.S. official said, as he works with regional allies to prevent the war from spiralling into a bigger conflict, and help win release of the hostages.

Gaza authorities said more than 2,300 people had been killed, a quarter of them children, and nearly 10,000 wounded. Rescue workers searched desperately for survivors of nighttime air raids. One million people had reportedly left their homes.

Israeli Prime Minister Benjamin Netanyahu's government also told the militant group Hezbollah, which neighbours Israel to the north, not to start a war on a second front, threatening the "destruction of Lebanon" if it did.

On Sunday, a senior Israeli official accused Iran of trying to open such a second front by deploying weapons in or through Syria, in a response to a post on social media platform X that posited such a scenario.

"They (Iranians) are," wrote Joshua Zarka, head of strategic affairs for Israel's foreign ministry.

Iran's mission to the United Nations warned late on Saturday that if Israel's "war crimes and genocide" were not halted immediately, "the situation could spiral out of control" and have far-reaching consequences.

Hamas and Hezbollah are backed by Iran.

Hamas leader Ismail Haniyeh, meeting Iran's foreign minister on Saturday in Qatar, discussed the Palestinian group's attack in Israel "and agreed to continue co-operation" to achieve the group's goals, Hamas said in a statement.

The Israeli military said that in an air strike in Khan Younis it killed a commander of Hamas' elite Nukhba Force who led the Oct. 7 attack on the two Israeli border villages of Nirim and Nir Oz.

U.S. President Joe Biden and other world leaders warned against any country broadening the conflict. International organisations and aid groups urged calm and pressed Israel to allow humanitarian assistance to get through.

In New York, Russia asked the U.N. Security Council to vote on Monday on a draft resolution on the Israel-Hamas conflict that calls for a humanitarian ceasefire and condemns violence against civilians and all acts of terrorism.

Warnings against wider conflict, calls for aid

Biden called Netanyahu on Saturday and, while reiterating "unwavering" support for Israel, discussed international co-ordination to ensure innocent civilians have access to water, food and medical care.

Biden also spoke with Palestinian President Mahmoud Abbas, who stressed the urgent need to allow humanitarian aid corridors in Gaza.

The U.S. Department of Defense said the Eisenhower aircraft carrier strike group would start moving towards the eastern Mediterranean to join another carrier strike group already there.

Defense Secretary Lloyd Austin said it was "part of our effort to deter hostile actions against Israel or any efforts toward widening this war following Hamas's attack on Israel."

On Friday, the Israeli military told residents of the northern half of the Gaza Strip, which includes the enclave's biggest settlement, Gaza City, to move south immediately.

On Saturday, it said it would guarantee the safety of Palestinians fleeing on two main roads until 4 p.m. (1300 GMT). Troops were massing as the deadline passed.

Hamas told people not to leave, saying roads out were unsafe. It said dozens of people had been killed in strikes on cars and trucks carrying refugees on Friday. Reuters could not independently verify this claim.

Some residents said they would not leave, remembering the "Nakba," or "catastrophe," when many Palestinians were forced from their homes during the 1948 war that accompanied Israel's creation.

"They are striking us but we are not going to leave our homes and we will not be displaced," said Shaheen, sitting at home with her grandchildren facing relentless Israeli bombardment and shortages of bread, drinking water and power.

Israel says Hamas is preventing people from leaving in order to use them as human shields, which Hamas denies.

The Palestinian Health Ministry said early on Sunday that 300 people, mostly children and women, had been killed, and 800 more had been injured in Gaza during the last 24 hours.

The only route out of Gaza not under Israeli control was a checkpoint with Egypt at Rafah.

Egypt officially says its side is open, but traffic has been halted for days because of Israeli strikes. Egyptian security sources said the Egyptian side was being reinforced and Cairo had no intention of accepting a mass influx of refugees.

A U.S. State Department official said the United States was working to open the crossing to let some people out, and had been in touch with Palestinian-Americans who want to leave Gaza.

Washington later said it had told its citizens to try to reach the crossing.

Israel says its evacuation order is a humanitarian gesture while it roots out Hamas fighters. The U.N. says so many people cannot be safely moved within Gaza without causing a humanitarian disaster.

Hezbollah warning

The violence in Gaza has been accompanied by the deadliest clashes at Israel's northern border with Lebanon since 2006, raising fears of war spreading to another front.

Hezbollah said it fired at five Israeli outposts in the disputed Shebaa Farms area with guided missiles and mortar bombs. Reuters saw missiles fired at an Israeli army post and heard shelling from Israel and gunfire.

Israel's Kan radio reported five border villages were under lockdown in response to a suspected incursion from Lebanon.

Netanyahu security adviser Tzachi Hanegbi said Israel was "trying not to be drawn into a two-front war" and warned Hezbollah to stay out of the fighting.