Israeli forces have killed at least 37 Palestinians along the Gaza border as demonstrators streamed to the frontier on the day the United States is opening its embassy in Jerusalem.
It marks the highest Palestinian single-day death toll since a series of protests dubbed the "Great March of Return" began at the border with Israel on March 30 and since a 2014 Gaza war.
Palestinian health officials say 900 Palestinians have been wounded, about 450 of them by live bullets.
Tens of thousands gathered at the frontier on Monday, some of them approaching Israel's border fence - a line Israeli leaders vowed Palestinians would not be allowed to breach. Black smoke from tyres set alight by demonstrators rose in the air.
"Today is the big day when we will cross the fence and tell Israel and the world we will not accept being occupied forever," said Gaza science teacher Ali, who declined to give his last name.
"Many may get martyred today, so many, but the world will hear our message. Occupation must end," he said.
Later in the day, Israeli leaders and a US delegation including Treasury Secretary Steven Mnuchin and President Donald Trump's daughter and son-in-law, Ivanka Trump and Jared Kushner, were due to attend the opening of the embassy relocated from Tel Aviv to Jerusalem.
"A great day for Israel," the US president, who stoked Arab anger by recognising Jerusalem as Israel's capital in December, said in a tweet.
Prime Minister Benjamin Netanyahu, in lockstep with Trump over fulfilling a long-standing US promise to move the embassy to the holy city and over the president's withdrawal from the Iran nuclear deal last week, echoed the sentiment.
"What a moving day for the people of Israel and the State of Israel," Netanyahu wrote on Twitter.
The 37 Palestinian dead on Monday included a 14-year-old boy, a medic and a man in a wheelchair who had been pictured on social media using a slingshot.
The Israeli military identified three of those killed as armed militants whom it said tried to place explosives near the fence in the southern Gaza Strip.
The latest casualties raised the Palestinian death toll to 73 since the protests started six weeks ago. No Israeli casualties have been reported.
"The IDF (Israel Defence Forces) will act forcefully against any terrorist activity and will operate to prevent attacks against Israelis," the military said in a statement.
The killings have drawn international criticism, but the US has echoed Israel in accusing Gaza's ruling Hamas movement of instigating violence, an allegation it denies.
Jason Greenblatt, Trump's Middle East peace envoy, said on Twitter that "taking the long-overdue step of moving our Embassy is not a departure from our strong commitment to facilitate a lasting peace deal. Rather, it is a necessary condition for it."
But Palestinian Prime Minister Rami Hamdallah accused the US of "blatant violations of international law".
The Palestinians, who want their own future state with its capital in East Jerusalem, have been outraged by Trump's shift from previous administrations' preference for keeping the US Embassy in Tel Aviv pending progress in peace efforts.