Jerusalem, Israel - President Joe Biden ordered US ships and warplanes to move closer to Israel in a show of support on Sunday, while sending new military aid to bolster operations against Gaza.

The Pentagon said it was sending the aircraft carrier USS Gerald R. Ford and its accompanying warships to the eastern Mediterranean, while boosting fighter aircraft squadrons in the region.

US Central Command confirmed Sunday afternoon that ships and planes had begun moving to their new posts.

At least four American citizens are known to have been killed in the violence so far, according to Senate Majority Leader Chuck Schumer.

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The White House moved quickly to affirm US backing for Israel after Saturday's surprise attack from the Gaza Strip, vowing "rock solid" support and warning other parties to stay out of the conflict.

Biden on Sunday spoke to Israeli Prime Minister Benjamin Netanyahu and "conveyed that additional assistance for the Israeli Defense Forces is now on its way to Israel with more to follow over the coming days," the White House said.

"The leaders also discussed ongoing efforts to ensure that no enemies of Israel believe they can or should seek advantage from the current situation," it said in a statement.

The US president further "pledged his full support for the Government and people of Israel in the face of an unprecedented and appalling assault by Hamas terrorists."

Hamas later accused the United States, a major supplier of arms to Israel, of "actual participation in the aggression against our people" by moving the aircraft carrier.

The Israeli-Palestinian conflict's worst escalation in decades has claimed more than 700 lives on the Israeli side, according to the military, while Gaza officials reported at least 400 deaths in Israeli air strikes.

Netanyahu has said there may be a long war ahead, with tens of thousands of Israeli forces already deployed to battle holdout Hamas forces and prepare a possible Gaza ground offensive.

With tensions rising, US Defense Secretary Lloyd Austin said he was sending forces to "bolster regional deterrence efforts" after discussions with Biden.

As well as the USS Gerald R. Ford carrier, this deployment includes a guided missile cruiser and four guided missile destroyers, Austin said in a statement.

"The United States government will be rapidly providing the Israel Defense Forces with additional equipment and resources, including munitions," added Austin, who also spoke with his Israeli counterpart on Sunday.

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The movement of US ships and planes and the aid to Israel "underscores the United States' ironclad support for the Israel Defense Forces and the Israeli people."

The United States on Sunday afternoon led calls for condemnation of the Hamas assault on Israel at the United Nations Security Council.

"I expect to hear from the other Council members very strong condemnation of these heinous acts of terrorism committed against the Israeli people and their government," senior US diplomat Robert Wood told reporters.

As the US government has pledged its continued military support for Israel, Palestinians on the ground fear for their lives.

Gaza, which has been described as the world's largest open-air prison, is the most densely populated places on the planet. Due to the Israeli blockade of the area, there are few, if any, opportunity for escape.

For decades, Palestinians in the Occupied Territories have been subjected to settler-colonial attacks, evictions, surveillance, and brutal repression of any form of resistance. In fact, the Israeli government has been described as an apartheid regime by prominent Israeli and international human rights groups.

Many Palestinians on the ground and their supporters around the world say the only way to stop the violence is to end the occupation and create a society that is truly inclusive and democratic for all.