US suspects several Americans either killed or taken hostages in Gaza

US government suspects that "several Americans" may be among those killed or taken hostage in Israel following attacks by Palestinian militants based in Gaza and following Israeli strikes, US Secretary of State Antony Blinken has said.

"We have reports that several Americans may be among the dead," Blinken told NBC's Meet the Press on Sunday, adding he was verifying the reports and also stories that some have been taken hostage.

On Saturday, the Palestinian movement Hamas ambushed Israel, firing rockets from Gaza as its fighters crossed over the border. Israel then carried out retaliatory strikes on the Gaza Strip, controlled by Hamas, declaring Israel was now "at war".

An Israeli military spokesperson said a "significant number" of Israeli civilians and soldiers were being held hostage in the Gaza Strip, with some presumed dead fuelling speculation that some American citizens might have been either killed or taken as hostages by the Hamas leaders.

"Women, children, elderly, disabled" civilians were "dragged into Gaza" in "unprecedented" numbers, IDF spokesperson Jonathan Conricus said on Saturday.

Blinken said Sunday the US is "working overtime" to verify reports of missing and dead Americans overseas after Hamas launched an unprecedented attack against Israel.

"We have reports that several Americans were killed. We're working overtime to verify that. At the same time, there are reports of missing Americans and there again, we're working to verify those reports," Blinken told CNN.

The surprise attack by Gaza militants on Israel on Saturday has left hundreds of Israelis dead, inviting retribution from Israeli Prime Minister Benjamin Netanyahu with a lethal volley of retaliatory Israeli airstrikes.

No one has a clue as yet how or when or what a full Israeli response would looke like. An Israeli military spokesperson however indicated that their forces may take full control of Gaza for the first time since 2005, even as 20 communities near Gaza were being evacuated.

Blinken has stated that additional aid to Israel in in the wake of the hamas attack may be announced as soon as Sunday.

"We're looking at specific additional requests that the Israelis have made – I think you're likely to hear more about that later today," Blinken said.

US President Joe Biden's direction is to "ensure" we're providing Israel everything it needs at this moment to deal with the attacks from Hamas.

Speaking from the White House Saturday, Biden said his administration's support of Israel's security is "rock solid and unwavering".

"When I spoke with Prime Minister Netanyahu this morning, I told him the US stands with the people of Israel in the face of these terrorist assaults. Israel has the right to defend itself and its people, full stop," he said.

Still, the president and his top aides are contending with a complicated diplomatic situation unlike any previous conflict between the Israelis and the Palestinians, the CNN reported.

Hamas spokesperson Abu Obeida said they had "dozens of captive officers and soldiers," continuing: "They have been secured in safe places and in the resistance tunnels" in the Gaza Strip.

The deputy chief of Hamas' political wing, Saleh al-Arouri, told a middle east news outfit that Hamas had "managed to kill and capture many Israeli soldiers", and that the number of Israeli hostages Hamas had captured was enough to release all Palestinian fighters in Israeli custody.

The US Embassy in Israel said on Saturday that it was "closely monitoring" the situation and that it was "aware that there have been casualties as a result of these incidents".

US citizens were directed to remain vigilant and take appropriate steps to increase their security awareness as incidents, including mortar and rocket fire, often take place without warning," the Embassy said in a statement, adding that US government personnel were not allowed to travel within seven miles of Gaza.

"Any American anywhere who is being detained or held hostage, that is going to be a priority for this government, this administration, and for me," Blinken said.

US President Joe Biden said Washington would "offer all appropriate means of support" to Israel after the "horrific and on-going attacks", adding that the US "unequivocally condemned this appalling assault against Israel by Hamas terrorists from Gaza".