Joe Biden on Tuesday declared support for Israel, calling the assault by Hamas militants that left nearly 1,000 people dead an “act of sheer evil” and confirming that some US citizens are part of the many currently being held hostage. In a televised speech from the White House, Biden said at least 14 Americans were killed in last weekend’s attack and an as yet unknown number of Americans are being held hostage. The attack saw gunmen crossing the border from Gaza, raiding Israeli cities and gunning down civilians in their homes, cars and at a desert music festival. As many as 150 hostages are believed to have been taken. More than 900 people in Gaza have been killed in retaliatory Israeli airstrikes. Jake Sullivan, the US national security adviser, said as many as 20 Americans are still missing after the violence on Saturday. He said the US is deploying experts and sharing intelligence with Israel as part of the US hostage recovery effort. “In this moment, we must be crystal clear: we stand with Israel,” Biden said in his speech, repeating: “We stand with Israel.” The US secretary of state, Antony Blinken, will travel to Israel in the coming days to echo the president’s message of solidarity, the state department announced on Tuesday. In his remarks from the White House State Dining Room, Biden was unequivocal in his condemnation of Hamas, calling it a terrorist organization whose “state purpose is the annihilation of the state of Israel and the murder of Jewish people”. “Hamas does not stand for the Palestinian people’s right to dignity and self-determination,” he added, echoing the sentiment expressed in a rare joint statement by the leaders of the US, UK, France, Germany and Italy on Monday night. “All of us recognize the legitimate aspirations of the Palestinian people,” it said. “But make no mistake: Hamas does not represent those aspirations, and it offers nothing for the Palestinian people other than more terror and bloodshed.” On Tuesday, Biden said the group’s attack “brings to mind the worst rampages of Isis.” “Parents butchered, using their bodies to try to protect their children. Stomach churning reports of babies being killed … women raped, assaulted, paraded as trophies,” he said. “This is terrorism.” Israel, Biden said, not only had the right to defend itself but a “duty” to do so. But in a phone call prior to his remarks, Biden said he reminded Israel’s prime minister, Benjamin Netanyahu, that democracies were more secure when they act “according to the rule of law”. Biden spoke as Israeli warplanes pounded the Gaza strip, part of a retaliation Netanyahu said would be so crushing that “what we will do to our enemies in the coming days will reverberate with them for generations.” Biden said the US was committed to supporting its ally and was “surging” additional military assistance to replenish its Iron Dome rocket interceptor system. The US Congress, presently plunged into chaos without a House speaker, may also be asked to take “urgent action” on the matter, Biden said. In Washington, the attack has largely drawn a similar response from lawmakers across the ideological spectrum, with condemnations of Hamas and expressions of solidarity with Israel. In a statement, the Senate leader Chuck Schumer, the highest ranking Jewish official in American history, said he spoke on Tuesday with Israel’s president Isaac Herzog and assured him that a bipartisan group in the US Senate “stands ready to do whatever it takes to ensure Israel has the resources it needs”. Still, there were voices of dissent. Congresswoman Rashida Tlaib, a Democrat from Michigan and the first Palestinian American woman elected to serve in Congress said in a statement: “I grieve the Palestinian and Israeli lives lost.” She also called on Israel to commit to “lifting the blockade, ending the occupation and dismantling the apartheid system that creates the suffocating, dehumanizing conditions that can lead to resistance”. She concluded: “As long as our country provides billions in unconditional funding to support the apartheid government, this heartbreaking cycle of violence will continue.” John Kirby, the White House National Security Council spokesman, told reporters that the US had already sent its “first tranche” of military assistance to Israel. He added that the US had no plans to put American military forces on the ground in Israel. State and federal law enforcement agencies in the US were also responding by taking steps to safeguard Jewish centers across the country and “disrupt any domestic threat that could emerge in connection to these horrific attacks”. Biden is a staunch ally of Israel, stretching back to his first visit to the country as a young US senator in 1973. In his remarks on Tuesday, Biden recalled that visit, 50 years ago, recounting a lengthy conversation he had with then Israeli prime minister Golda Meir in the weeks leading up to the Yom Kippur war. He said Meir, sensing his concern for the fate of Israel, sought to assure him. “Don’t worry, Senator Biden, we have a secret weapon,” she whispered, according to Biden. “We have no place else to go.”