SDEROT, Oct 8 (AFP) - Israel, reeling from the deadliest ever attack on its territory, declared war on Hamas on Sunday (Oct 8) as the conflict's death toll surged above 1,000 after the Palestinian militant group launched a massive surprise assault from Gaza.

Prime Minister Benjamin Netanyahu steeled the shocked and grieving nation for a "long and difficult" war a day after Hamas fired a barrage of thousands of rockets at Israel and sent a wave of fighters who gunned down civilians and took at least 100 hostages.

More than 700 Israelis have been killed since Hamas launched its large-scale attack, according to the latest toll from the Israel Defense Forces (IDF) on Monday - the country's worst losses since the 1973 Arab-Israeli war.

"Israel was caught flat-footed by the unprecedented attack," said Jonathan Panikoff, director of the Scowcroft Middle East Security Initiative. "I've heard multiple comparisons to 9/11, and many Israelis are struggling to understand how this could have happened."

Gaza officials reported at least 413 deaths in the impoverished and blockaded enclave of 2.3 million people, which was hammered by Israeli air strikes on 800 targets ahead of what many feared may be a looming ground invasion.

US President Joe Biden ordered "additional support for Israel in the face of this unprecedented terrorist assault by Hamas".

A US National Security Council spokesperson confirmed that "several" Americans had been killed in the surprise attack, but did not provide further details.

US Defense Secretary Lloyd Austin said Washington "will be rapidly providing the Israel Defense Forces with additional equipment and resources, including munitions".

Austin also said he had directed the USS Gerald R Ford aircraft carrier and group of warships to the eastern Mediterranean, and that Washington was augmenting fighter aircraft squadrons in the region.

Hamas has said the US aid amounted to "aggression" against Palestinians.

Several foreign countries have reported nationals killed, abducted or missing in the fighting, among them Brazil, Britain, France, Germany, Ireland, Mexico, Nepal, Thailand and Ukraine.

Tens of thousands of Israeli forces were deployed to battle holdout Hamas fighters in the south, where the bodies of civilians had been found strewn on roads and in town centres.

"The enemy is still on the ground," said military spokesman Daniel Hagari as a second night fell after the massive opening attack.

Gun battles raged as the Israeli army sought to secure desert regions near the coastal enclave, rescue hostages and evacuate all areas near Gaza, after the cabinet formally declared war by activating Article 40 of the Basic Law.

"We'll reach each and every community until we kill every terrorist in Israel," vowed Hagari, a day after Hamas fighters surged into Israel using vehicles, boats and motorised paragliders.

Photo from AFP