US Secretary of State Antony Blinken headed Wednesday to Israel in a show of solidarity after a bloody attack by Hamas, with Washington closing ranks with its ally as it launched heavy retaliation on the Gaza Strip.

Blinken was set to arrive Thursday in Israel for a lightning visit in which he is likely to see Prime Minister Benjamin Netanyahu, who has vowed an unrelenting response to what he called the Islamist militants' "savagery."

President Joe Biden said Wednesday that he had just made another phone call to Netanyahu and he reiterated "unshakeable" US support.

The State Department, meanwhile, said that the known death toll of US citizens in the violence had risen to "at least 22." A so-far unspecified number of American hostages are also believed to be in the hands of Hamas.

In a departure from usual US calls for restraint when violence erupts overseas, Biden and his administration have made clear they support Israel's right to an overwhelming response.

In a speech Tuesday, Biden showed visible emotion as he addressed the Hamas attack, which included killings of children, music festival revelers and other civilians, and has triggered a war in which the death toll is steadily rising on both sides.

"There are moments in this life -- I mean this literally -- when a pure unadulterated evil is unleashed on this world," said Biden, flanked by Blinken and Vice President Kamala Harris.

Blinken's spokesman, Matthew Miller, made clear that the top US diplomat will not be pressuring Israel and instead will lock arms with Netanyahu, who has had a rocky relationship in the past with Biden and other Democrats in part over his opposition to Palestinian sovereignty.

Blinken will "reaffirm the United States' solidarity with the government and people of Israel," Miller said.

"He will also discuss measures to bolster Israel's security and underscore the United States' unwavering support for Israel's right to defend itself," he said.

US officials, however, have said that they see the fight being against Hamas, not the Palestinian people, and they welcomed a European Union about-face on cutting off development aid for the Palestinians.

Israel has announced that it is shutting down food, electricity and water for the Gaza Strip, the densely populated and impoverished territory governed by Hamas and under an Israeli blockade since 2007.

Blinken will head from Jerusalem to Jordan, a close US partner which has a peace treaty with Israel and historically has been concerned over shake-ups in the Palestinian territories.

- Turning page with Netanyahu -

Further complicating the policy options for both the United States and Israel is that Hamas has taken large numbers of hostages and is threatening to kill them. Biden has said that an unspecified number of the hostages hold US citizenship.

Biden has earlier criticized Netanyahu over his hard-right government's deeply controversial overhaul of the judiciary and its defiant pursuit of Jewish settlements in the occupied West Bank.

Those disputes now appear to be in the past or at least on the back burner, with Netanyahu on Wednesday reaching a deal for a wartime emergency government with opposition leader Benny Gantz.

Logan Bayroff of J Street, a liberal pro-Israel group often critical of Netanyahu, praised the administration's support for Israel after "one of the most horrific massacres of civilians anywhere in the 21st century."

But he said that Netanyahu has shown "his legacy at this point is one of complete failure" and that the administration needed a longer-term solution to the Palestinian issue.

"The Israeli-Palestinian conflict remains one of the most deadly and dangerous and active conflicts in the region and in fact the entire world, and resolving the conflict head-on has to be a high priority for the Biden administration," he said.

The rival Republican Party has also attacked Biden over the violence, especially due to his quiet diplomacy with Iran, which openly supports Hamas.

Two centrist senators from Biden's own Democratic Party, Jon Tester and Joe Manchin, have called for a re-freeze of $6 billion in Iranian oil revenue that was transferred in a deal to free US prisoners.

The Biden administration says the money, which had been blocked by South Korea, has not however been dispensed and is restricted to humanitarian use.

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