Israeli forces have killed at least 18 Palestinians during mass protests along the Gaza border, casting a cloud over the inauguration of the new US embassy in Jerusalem.
It is the deadliest single day of protests since the Palestinians began staging weekly border demonstrations on March 30 in an attempt to break an Israeli-Egyptian blockade.
Protesters set tyres on fire, sending thick plumes of black smoke into the air, while the Israeli military accused protesters of trying to break through the border fence and plant a bomb. They also claimed troops had come under fire.
By mid-afternoon on Monday, at least 18 Palestinians - including a 14-year-old boy - were killed, while more than 500 were wounded by Israeli gunfire, Palestinian health officials said.
In the West Bank, several thousand people gathered in the centre of Ramallah, while hundreds marched to the Qalandiya crossing on the outskirts of Jerusalem, where protesters threw stones at Israeli troops.
The protest in Gaza is the biggest yet in a weeks-long campaign against a decade-old blockade of the territory. The march was also directed at the inauguration of the US embassy in Jerusalem later.
The relocation of the embassy from Tel Aviv, a key campaign promise of US president Donald Trump, has infuriated the Palestinians, who seek east Jerusalem as a future capital.
"A great day for Israel!" Trump tweeted earlier on Monday.
The showdown between Israel's military and Gaza's Hamas rulers along the volatile border is the culmination of a campaign, fuelled by despair among Gaza's two million people, to break the decade-old border blockade of the territory imposed by Israel and Egypt after Hamas seized control of Gaza in 2007.
Since weekly border marches began in late March, 60 Palestinian protesters have been killed and more than 2,300 were wounded by Israeli army fire.
Hamas leaders have suggested a border breach is possible on Monday, while Israel has warned it would prevent protesters from breaking through the barrier at any cost.
Most of the casualties were in the southern Gaza towns of Khan Younis and Rafah. Israeli forces were firing volleys of tear gas to disperse the crowds, and the sound of heavy gunfire could be heard. Sirens were constantly wailing as the wounded were evacuated on stretchers to nearby ambulances. Groups of young activists repeatedly approached the fence, but were quickly scattered by gunfire and tear gas.
The timing of Monday's events is deeply symbolic to both Israelis and Palestinians.
The US said it chose the date to coincide with the 70th anniversary of Israel's establishment.
But it also marks the anniversary of what Palestinians call their "nakba", or catastrophe, a reference to the uprooting of hundreds of thousands who fled or were expelled from what is now Israel during the 1948 war surrounding Israel's independence.