The US on Monday opened its embassy in Jerusalem amid violent clashes along the Gaza Strip's border hours ahead of the controversial move, leaving 37 Palestinians dead from Israeli fire and hundreds more wounded, the deadliest escalation of violence since 2014.
The Gaza Health Ministry said 37 Palestinians were killed by Israeli fire amid mass protests on the border against the transfer of the US embassy from Tel Aviv to Jerusalem.
The dead included a 14-year-old, according to the ministry.
Meanwhile, the Palestinian Authority government accused Israel of committing a "terrible massacre" after Israeli fire killed 37 Palestinians in protests and clashes.
Palestinian government spokesman Yusuf al-Mahmoud demanded in a statement "an immediate international intervention to stop the terrible massacre in Gaza committed by the forces of the Israeli occupation against our heroic people."
Thousands had gathered near the border in protest while smaller numbers of stone-throwing Palestinians were approaching the fence and trying to break through, with Israeli snipers positioned on the other side.
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Crowds built throughout the day in the Palestinian enclave less than 100 kilometres away from Jerusalem and sealed off from Israel by a blockade.
Israel's military said "approximately 10,000 violent rioters are currently assembled in a number of locations along the Gaza Strip border and thousands more are gathered by the tents approximately half a kilometre away from the security fence."
It said soldiers "are responding with riot dispersal means and fire, and are operating according to standard operating procedures." The inauguration that follows US President Donald Trump's deeply controversial December 6 recognition of the disputed city as Israel's capital also comes at a time of heightened regional tensions.
It follows Trump's announcement last week that the United States is withdrawing from the Iran nuclear deal and Israeli strikes two days later on dozens of Iranian targets in Syria.
Those strikes came after rocket fire toward Israeli forces in the occupied Golan Heights that Israel blamed on Iran.
The Trump administration has vowed to restart the moribund Middle East peace process but the embassy move has inflamed tensions.
On Sunday, Al-Qaeda leader Ayman al-Zawahiri released a message saying America's decision was evidence that "appeasement" has failed Palestinians and urged Muslims to carry out jihad against the United States, according to a transcript provided by the SITE monitoring agency.
Monday's inauguration ceremony at 4:00 pm (1300 GMT) will include around 800 guests -- though not Trump himself -- at what until now had been a US consulate building in Jerusalem.
US Deputy Secretary of State John Sullivan will lead the Washington delegation that includes Trump's daughter Ivanka and her husband Jared Kushner, both White House aides, as well as Treasury Secretary Steven Mnuchin.
Israeli Prime Minister Benjamin Netanyahu, who has repeatedly called Trump's decision "historic", welcomed them at a reception on Sunday.
"Jerusalem has been the capital of the Jewish people for the past 3,000 years," he said.
"It's been the capital of our state for the past 70 years. It will remain our capital for all time." Sullivan called the embassy "a long overdue recognition of reality." Saeb Erekat, Palestine Liberation Organisation secretary-general, called it a "hostile act against international law".
Around 1,000 police officers were being positioned around the embassy for the inauguration.
Israel's army said it was almost doubling the number of troops surrounding Gaza and in the occupied West Bank.
It also dropped leaflets warning Gazans to stay away from the fence, including one with a photo of the Champs-Elysees boulevard in Paris and the caption: "Gaza 2025? The choice is in your hands." Israeli Defence Minister Avigdor Lieberman said in a message to Gazans "we will protect our civilians with all our means and not enable the fence to be crossed." Israelis began celebrating on Sunday, as tens of thousands of marched in Jerusalem, some holding American flags, to mark Jerusalem Day.
The annual event is an Israeli celebration of the "reunification" of the city following the 1967 Six-Day War.
Israel occupied the West Bank and east Jerusalem in 1967 and later annexed east Jerusalem in a move never recognised by the international community.
Beyond the disputed nature of Jerusalem, the date of the embassy move is also key.
May 14 marks the 70th anniversary of the founding of Israel.
The following day, Palestinians mark the "Nakba", or catastrophe, commemorating the more than 700,000 Palestinians who fled or were expelled from their homes in the 1948 war surrounding Israel's creation.
Palestinian protests are planned on both days.
There have already been weeks of protests and clashes along the Gaza border, with 70 Palestinians killed by Israeli fire there since March 30.
No Israelis have been wounded and the military has faced criticism over the use of live fire.
Trump calls Jerusalem embassy move 'a great day for Israel'
US President Donald Trump on Monday hailed the scheduled opening of the US embassy in Jerusalem as "a great day for Israel."
Trump made no reference to the violence in an early morning tweet, instead inviting Twitter followers to watch live coverage of the embassy opening on Fox News channels, which was to begin at 1300 GMT.
"Lead up to 9:00 A.M. (eastern) event has already begun. A great day for Israel!" Trump tweeted.
Arabs, Muslims condemn US Embassy move
The Arab League and the top Sunni Muslim religious authority have criticized the relocation of the U.S. Embassy from Tel Aviv to contested Jerusalem.
The Cairo-based Arab League called on the international community to oppose what it considers an "unjust decision" and the ongoing "Israeli occupation" of the city.
It called the move a "blatant attack on the feelings of Arabs and Muslims," and a "grave violation of the rules of international law" that would destabilize the region.
The Palestinians, who claim east Jerusalem as the capital of their future state, have called for an urgent meeting at the Arab League on Wednesday to discuss the matter.
Egypt's Al-Azhar religious institution called on the international community to use "all peaceful means" to "dismiss positions of countries that sided with the Zionist entity," referring to Israel.
Trump calls Jerusalem embassy move 'a great day for Israel'
US President Donald Trump on Monday hailed the scheduled opening of the US embassy in Jerusalem as "a great day for Israel."
Trump made no reference to the violence in an early morning tweet, instead inviting Twitter followers to watch live coverage of the embassy opening on Fox News channels, which was to begin at 1300 GMT.
"Lead up to 9:00 A.M. (eastern) event has already begun. A great day for Israel!" Trump tweeted.