At least 37 Palestinians were killed Monday and more than 900 wounded as protests at the Gaza border with Israel turned deadly ahead of the U.S. Embassy opening in Jerusalem, Palestinian health officials said.

The bloodiest day in weeks of demonstrations could become even more chaotic as Israel vows to hold back thousands of protesters and prevent the possibility they could breach the border at any cost. Over 35,000 protesters at 12 locations have amassed along the Gaza security fence.

The violent clashes threaten to overshadow a historic moment for the U.S. and Israel, as the U.S. Embassy is officially moved from Tel Aviv to Jerusalem.

The relocation of the embassy had been a key campaign promise of President Trump, and he sent a high-level delegation including his daughter Ivanka and son-in-law Jared Kushner to mark the occasion.

"A great day for Israel," Trump tweeted early Monday.

But infuriated Palestinian protesters gathered in huge numbers to condemn the move, drawing Israeli fire at the Gaza border. Protesters set fire to tires, sending thick plumes of smoke into the air along several spots.

Monday marked the biggest showdown between Israel’s military and Gaza’s Hamas rulers along the volatile border.

Earlier Monday, Treasury Secretary Steve Mnuchin said the Trump administration’s decision to relocate the Israel embassy from Tel Aviv to Jerusalem is a “national security priority” for the U.S.

Mnuchin came to Jerusalem ahead of the opening ceremony for the new U.S. Embassy as part of a 250-member delegation, including Ivanka Trump and Kushner, U.S. Deputy Secretary of State John Sullivan, U.S. Ambassador to Israel David Friedman and Middle East envoy Jason Greenblatt

Mnuchin will unveil the plaque officially recognizing the embassy in Jerusalem, according to the Times of Israel.

“I'm thrilled to be here on behalf of the president. It's a big day - moving the embassy here. Seventy years in the making. We're thrilled to be here representing the president to do this,” Mnuchin said.

Israel prepared enthusiastically Sunday for the formal embassy opening with a gala party at its Foreign Ministry that included Ivanka Trump, Jared Kushner and other U.S. officials.

Israeli Prime Minister Benjamin Netanyahu told revelers that Trump's December declaration recognizing Jerusalem as Israel's capital was "the right thing to do."

"Thank you, President Trump, for your bold decision. Thank you for making the alliance between Israel and the United States stronger than ever,” he said.

The prime minister said Trump's decision recognized a 3,000-year Jewish connection to Jerusalem and the "truth" that Jerusalem would be Israel's capital under any future peace deal.

Meanwhile, Israel bolstered its border security as thousands of Gaza residents headed toward the Israeli border. Since weekly border marches began in late March, dozens of Palestinian protesters have been killed and more than 2,000 wounded by Israeli army fire.

Hamas leaders have suggested a possible border breach in the days leading up to the embassy celebration, while Israel has warned it would prevent protesters from breaking the border.

Palestinian officials have criticized the Trump administration for its decision to move the U.S. Embassy to Jerusalem. Palestinian President Mahmoud Abbas cut ties with the U.S., declaring it unfit to be the sole mediator for potential peace between Israel and Palestine.

The Trump administration had brushed off Palestinian criticism, saying that the embassy move could be a first step for brokering a peace agreement.

Fox News’ Samuel Chamberlain and the Associated Press contributed to this report.