* US opening Jerusalem embassy later in the day
* Thousands of Palestinians gather at Gaza border
* Part of six-week "right of return" protest
* Israel vows to prevent border breach
Israeli troops killed at least 16 Palestinians along the Gaza border on Monday, health officials said, as demonstrators streamed to the frontier on the day the United States prepared to open its embassy in Jerusalem.
Protests intensified on the 70th anniversary of Israel's founding, with loudspeakers on Gaza mosques urging Palestinians to join a "Great March of Return". Black smoke from tyres burned by demonstrators rose into the air at the border.
"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.
Israeli troops killed 16 Palestinians, including a 14-year-old boy on Monday, and some 500 protesters were injured, at least 200 by live bullets, health officials said.
The latest casualties raised the Palestinian death toll to 61 since the protests began on March 30. No Israeli casualties have been reported.
The killings have drawn international criticism, but the United States, which has angered the Palestinians and Arab powers by relocating its embassy to Jerusalem from Tel Aviv, has echoed Israel in accusing Gaza's ruling Hamas movement of instigating violence, an allegation it denies.
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.
"What a moving day for the people of Israel and the State of Israel," Israeli Prime Minister Benjamin Netanyahu wrote on Twitter.
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 said Trump's recognition of Jerusalem as Israel's capital in December and the relocation of the embassy were "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.
Those talks have been frozen since 2014. Other major powers worry that the US move could also inflame Palestinian unrest in the occupied West Bank, which Israel captured along with East Jerusalem in a 1967 war.
Israel's military dropped leaflets into the enclave on Monday, warning Palestinians "not to serve as a tool of Hamas" or approach or damage Israel's frontier fence.
But thousands of Palestinians massed at five locations along the line. Of the 35 people wounded by Israeli gunfire, four were journalists, the officials said.
The Israeli military says its troops are defending the border and firing in accordance with the rules of engagement.
"We are prepared to face the Hamas threats to disrupt the (embassy) festivities," Israeli Defence Minister Avigdor Lieberman tweeted.
"My recommendation to the residents of Gaza: Don't be blinded by (Hamas's Gaza leader, Yehya Al-) Sinwar, who is sending your children to sacrifice their lives without any utility. We will defend our citizens with all measures and will not allow the fence to be crossed."
The protests are scheduled to culminate on Tuesday, the day Palestinians mourn as the "Nakba" or "Catastrophe" when, in 1948, hundreds of thousands of them were driven out of their homes or fled the fighting around Israel's creation.
"Choosing a tragic day in Palestinian history (to open the Jerusalem embassy) shows great insensibility and disrespect for the core principles of the peace process," Hamdallah wrote.
Most countries say Jerusalem's status should be determined in a final peace settlement, and that moving their embassies now would prejudge any such deal.
But Guatemala plans to open an embassy in Jerusalem on Wednesday, and its ambassador visited the new site, in an office building in the western part of the city on Monday. Paraguay is to follow suit later this month.