Washington DC - Israeli Prime Minister Benjamin Netanyahu asked for unity from lawmakers Wednesday as he addressed a US Congress divided by his unrelenting assault on the people of Gaza, with a rift between the nations deepening over the conflict's horrific humanitarian toll.

Washington has become increasingly critical of Israel's nine-month war in the narrow coastal territory, while protests in Israel by families of hostages taken by Hamas are also causing headaches for Netanyahu at home.

Amid empty seats as some US lawmakers skipped the speech in protest of the ongoing assault on Gaza, the Israeli leader got a rousing welcome from Republicans as he entered the historic chamber.

"For the forces of civilization to triumph, America and Israel must stand together," Netanyahu said in his address.

"The day after we defeat Hamas, a new Gaza can emerge. My vision for that day is of a demilitarized and deradicalized Gaza," he continued.

"Israel does not seek to resettle Gaza. But for the foreseeable future, we must retain overriding security control there to prevent the resurgence of terror, to ensure that Gaza never again poses a threat to Israel... Gaza should have a civilian administration run by Palestinians who do not seek to destroy Israel."

Netanyahu then took aim at Hamas' sponsor, Iran.

"Our world is in upheaval. In the Middle East, Iran's axis of terror confronts America, Israel, and our Arab friends," Netanyahu said.

"This is not a clash of civilizations. It's a clash between barbarism and civilization."

Outside the US Capitol, thousands of protesters tried to march on the seat of the US government but were kept at least a block away by police who fired pepper spray, and the rally ultimately dispersed.

Netanyahu drew boos when he criticized protesters as "Iran's useful idiots," but then doubled down and suggested that they were being directly financed by the Islamic Republic.

His visit came at a time of political upheaval in the US, with a gunman targeting Republican candidate Donald Trump and President Joe Biden bowing out of the 2024 White House race and endorsing his deputy, Kamala Harris.

Biden will meet Netanyahu on Thursday, the White House said, to discuss progress towards a ceasefire and a hostage release deal, as well as Washington's "ironclad commitment to Israel's security."

Harris will hold separate talks with the Israeli leader on Thursday but did not attend his speech due to previously scheduled travel.

Addressing the vice president's absence, an Israeli government spokesman said the speech was "bigger than any individual."

Netanyahu will also meet with Trump – with whose administration he had a much less fraught relationship than Biden's – in Florida on Friday.

"I... want to thank President Trump for all the things he did for Israel. From recognizing Israel's sovereignty over the Golan Heights to confronting Iran's aggression to recognizing Jerusalem as our capital and moving the American embassy there," Netanyahu told US lawmakers, referring to steps Trump took while in office.

And "I want to thank President Biden for his tireless efforts on behalf of the hostages," he said, referring to people seized by Hamas during the October 2023 attack.

Republican Speaker of the House Mike Johnson said Tuesday that with Israel facing attacks from various Iranian proxies, "it has never been more important than it is right now to stand with our closest ally in the Middle East."

But about half of the Democratic lawmakers boycotted on Netanyahu's address, including independent Senator Bernie Sanders, who said Tuesday that "Netanyahu should not be welcomed into the US Congress."

Several other senior Democrats – from Senate number two Dick Durbin to influential former House speaker Nancy Pelosi – joined multiple members of the rank-and-file in announcing they would be skipping the speech.

Hours before the address, scores of protesters started gathering downtown, where Palestinian flags had been taped to street lights.

They waved banners calling on America to "End all US aid to Israel" and assailing Netanyahu as a "war criminal" alongside a mugshot of the Israeli premier, who is facing an arrest warrant from the International Criminal Court over Israel's mass killing and starvation of Palestinians.

Israel has recently intensified its attacks on Gaza, and Netanyahu has claimed that only piling on military pressure can free the hostages and defeat Hamas.

The group's shock attack on October 7 resulted in the deaths of 1,197 people, mostly civilians, according to an AFP tally based on Israeli figures.

Israel's retaliatory military campaign in Gaza has killed at least 39,090 people, also mostly civilians, according to figures from the occupied territory's health ministry – though the true death toll is likely to be much higher.

Publicly, Biden has voiced strong support for Israel. But he expressed concern over an offensive on the southern Gaza city of Rafah and suspended a shipment of 2,000-pound bombs to Israel over fears that they would be used in populated areas.

Despite the mounting death toll in Gaza, the US has continued to defend Israeli interests while taking a key role in mediation efforts, and the countries' military relationship remains strong, officials say.

But Council on Foreign Relations Middle East specialist Steven Cook said that "never before has the atmosphere been so fraught."

"There is clearly tension in the relationship, especially between the White House and the Israeli prime minister," Cook said.