Washington DC - Thousands of protesters in the US capital on Saturday called for a ceasefire in Gaza amid Israel's relentless bombing campaign, with some slamming President Joe Biden's support for Washington's top ally in the Middle East.

The rally, at which demonstrators waved Palestinian flags and wore the traditional keffiyeh scarf, was the largest protest in Washington since the beginning of the Israel-Hamas conflict on October 7.

"Free, free Palestine," and "End the siege on Gaza now," the protesters shouted.

Other slogans targeted the president: "Biden, Biden, you can't hide, you signed off on genocide" and "We say no, Genocide Joe."

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"It is unacceptable to allow for the loss of so many innocent lives, and we cannot consider this a proportional conflict," said 24-year-old Amanda Eisenhour of Virginia.

"This is a massacre, a genocide... a stain on our history, and I cannot accept as a citizen that my taxes are funding this."

Jasmine Iman (25) came from New York to attend the protest and said she would not vote for Biden in next year's presidential election because of his steadfast support for Israel.

"We will not vote for the Democratic Party. We will make sure that everyone we know knows not to vote for the Democratic Party because of (Gaza)," she said.

Biden (80) is likely to face off against 77-year-old Republican former president Donald Trump a year from now, with polls showing a hypothetical matchup in a virtual dead heat.

If the election ends up being a choice between Biden and Trump, "I'll sit it out," Iman said.

Fighting raged in Gaza on Saturday for the 29th day since Hamas militants stormed across the Israeli border and, according to Israeli officials, killed more than 1,400 people, mostly civilians, and abducted over 240 others.

Since then, Israel has relentlessly bombarded the Gaza Strip and sent in ground troops. The health ministry in the Palestinian territory says 9,488 people have been killed, around two-thirds of them women and children.