In the deadliest day of violence in Gaza since the 2014 war, Palestinian officials say Israeli troops have killed 55 people and wounded 2,700.
Israeli PM Benjamin Netanyahu said his military was acting in self-defence against Gaza’s Islamist rulers, Hamas, who he said wanted to destroy Israel.
The Palestinian Authority’s leader condemned a “massacre”. The UN spoke of “outrageous human rights violations”.
The violence came as the US opened a controversial embassy in Jerusalem.
The move of the US embassy from Tel Aviv has incensed Palestinians, who claim eastern Jerusalem as the capital of a future Palestinian state.
They see the US move as backing Israeli control over the whole of the city, which Israel regards as its indivisible capital.
What happened at the Gaza border?
Palestinians were demonstrating on Monday as they have been for six weeks as part of a protest, orchestrated by Hamas, called the “Great March of Return”.
However, Monday’s protests – and more planned for Tuesday – are the culmination, as they mark the anniversary of Israel’s creation in 1948 and what Palestinians term the Nakba or Catastrophe, referring to the hundreds of thousands of their people who subsequently fled their homes or were displaced in the war that followed.