With senior members of Congress addressing the event on the National Mall, near the Capitol, the crowd rapidly swelled with people wearing the white and blue colors of Israel and waving placards calling on Palestinian militant group Hamas to free hostages.
Despite fierce controversy in the United States over the intensity of the Israeli military response to the October 7 surprise cross-border attack by Hamas, rally goer Sergei Kravchick, said, "We of course support Israel.... We're doing exactly what we have to do."
Kravchick, 64, said he was "proud" to see the large turnout.
The demonstration, dubbed the March for Israel, centered on combating anti-Semitism and calling for the release of the 240 hostages held by Hamas, according to the Jewish Federation of Greater Washington, one of the organizers.
Hamas fighters stormed across the border from the Gaza Strip, killing around 1,200 people, most of them civilians, according to Israeli officials.
Since then, the Israeli army has heavily bombarded Gaza and launched a ground invasion, killing more than 11,200 people, mostly civilians, according to the health ministry in Hamas-run Gaza. The heaviest fighting has centered around Gaza hospitals.
Speaking by video link from Jerusalem, Israeli President Isaac Herzog told the crowd they were "marching for the right of every Jew to live proudly and safely in Israel and the US and the world."
"No one will break us," he said.
US Senate Majority Leader Chuck Schumer -- a Democrat -- and House Speaker Mike Johnson -- a Republican -- also spoke, as well as family members of the hostages.
"America feels your pain," Schumer, the highest-ranking Jewish elected official in the United States.
Heavy police presence
The demonstration comes after multiple large protests around the country -- and in cities around the world -- calling for a ceasefire and criticizing the Israeli military.
Security was tight, reflecting the wider tensions.
Police stationed snowplows as temporary roadblocks nearby and a military style armored vehicle was also deployed. Protesters' bags were searched before being allowed to enter the area.
In contrast to pro-Palestinian demonstrations from New York to Los Angeles that have focused on the suffering of civilians in Gaza, Tuesday's crowd turned its anger on Hamas.
Signs included "Annihilate Hamas" and "From the river to the sea, we support democracy."
Mark Moore, 48, a Christian pastor from Chicago, said he considers Israel "the only bastion of freedom" in the Middle East and that although he wanted peace ultimately, "I'm praying for peace... secured through victory so it does not continue with this endless cycle of violence."
Less than two weeks ago, a major pro-Palestinian demonstration took place in Washington, with a large crowd marching up to the fence around the White House, protesting against President Joe Biden's staunch support for Israeli military policies.
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