At least 58 Palestinians were reported killed by Israeli troops in clashes on the Gaza border, as the United States took the controversial step of opening an embassy in Jerusalem.
Gaza's Health Ministry said that 2,700 Palestinians were also wounded by live gunfire, tear gas, or other means on May 14 -- the bloodiest day of clashes since the 2014 Gaza war.
Israel said some 40,000 Palestinians took part in "violent riots" along the Gaza Strip security fence. Prime Minister Benjamin Netanyahu defended the use of force, saying that "every country has the obligation to defend its borders."
Palestinian Authority President Mahmud Abbas condemned what he called "massacres" carried out by Israeli troops, and declared three days of mourning.
UN human rights chief Zeid Ra'ad al-Hussein denounced "outrageous human rights violations" by Israeli forces.
White House spokesman Raj Shah said “the responsibility for these tragic deaths rests squarely with Hamas.”
A number of other Western nations called for restraint.
Palestinians have been demonstrating for six weeks as part of a protest orchestrated by the Islamist movement Hamas, which has been ruling Gaza since 2007.
The latest violence coincided with the state of Israel's 70th anniversary and the dedication ceremony for a U.S. embassy in Jerusalem.
Trump announced last year that the United States was recognizing the divided city as the capital of Israel and would move its Embassy in Israel from Tel Aviv to Jerusalem, creating an outcry from Palestinians, U.S. allies, and many other countries worldwide.
Palestinians want East Jerusalem to be the capital of their future state. Israel has annexed East Jerusalem and declared the entire city as its capital, a move not recognized by the international community.
Top U.S. officials, including President Donald Trump's daughter Ivanka Trump, attended the event, as hundreds of Arab citizens of Israel staged a protest near the site of the new U.S. Embassy.
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U.S. Embassy Opens In Jerusalem
In a recorded message at the ceremony, President Trump said he remained "fully committed" to pursuing peace between Israel and the Palestinians.
"Our greatest hope is for peace," he said.
Netanyahu thanked Trump for "having the courage" to keep his promise to move the embassy to Jerusalem, which he called the "eternal, undivided capital of Israel."
Abbas reiterated his condemnation of the U.S. embassy move, saying he "will not accept" any peace deal proposed by the Trump administration.
Arab League Secretary-General Ahmed Abul Gheit blasted as "shameful" the countries that are celebrating the opening of the U.S. Embassy in Jerusalem.
Iran's foreign minister called the move "a day of great shame."
The U.S. Consulate in Jerusalem will serve as an interim office for the U.S. ambassador to Israel along with a small number of staff. A larger site will be built later when the rest of the embassy moves from Tel Aviv.