Washington: In his latest show of support for Israel, US President Joe Biden on Wednesday addressed Jewish community leaders at a roundtable in the White House and called the attacks by Hamas a "campaign of pure cruelty".

"I never really thought that I would see and have confirmed pictures of terrorists beheading children," Biden said in broader remarks about his administration's support for Israel amid its war with Hamas and efforts to free American hostages.

During the event at the White House, featuring a group of around two dozen rabbis and leaders of Jewish organisations, Biden also warned Iran to "be careful".

"We moved the US carrier fleet to the eastern Mediterranean and we are sending more fighter jets to that region, and made it clear to the Iranians: Be careful," he said, adding, "When terrorist groups like Hamas, brought not only a sheer evil, sheer evil to the world, evil that echoes the worst matches in some cases exceeds the worst atrocities of ISIS."

Earlier on Wednesday, the US president spoke to Israeli Prime Minister Benjamin Netanyhu, marking the fourth known call between the two. Biden also assured Netanyahu that the United States is sending more military assistance to help Israel fight Hamas militants.

"The United States has Israel's back and I have yours as well - both at home and abroad," the president said.

On Tuesday, Biden confirmed that US citizens are among those who have been taken hostage by Hamas. The White House said on Wednesday that 17 Americans are unaccounted.

Meanwhile, US State Department Secretary, Antony Blinken called the Hamas attacks as "appalling," and also reiterated US support for Israel. He said at least 22 US citizens have been killed in the attacks.

"The terrorist attacks against Israel are appalling, and the world should be revolted at what it's seen. As we continue to closely monitor the situation, we sadly now know that at least 22 US citizens were killed, and US citizens are among those being held by Hamas," posted Blinken on X, adding, "We join families in Israel, in the US, and around the world mourning the loss of loved ones killed in Hamas's heinous attacks. We continue efforts to secure the release of those hostages, and the US remains steadfast and unwavering in our support for Israel."

In a major escalation on October 7, Hamas launched a "surprise attack" on Israel, firing a barrage of rockets into the southern and central parts of the country.

On Wednesday, the Israel Defence Force (IDF) spokesperson Lieutenant Colonel Jonathan Conricus said that 1,200 Israelis have been killed and over 2,700 wounded while emphasising that the Israeli soldiers are ready to execute the mission in Gaza.

As the US administration continues its efforts to support Israel and deploy military assets to the region, various US government agencies are working behind the scenes to construct an accurate assessment of the situation on the ground.

In the wake of deadly Hamas attacks on Israel, the US State Department has advised Americans to reconsider travelling to Israel. The travel advisory for the West Bank has also been raised to level 3, while the advisory for Gaza remains at the most severe - "Level 4: Do Not Travel."