Reports say at least 58 Palestinians in Gaza have been shot dead by Israeli troops after bloody clashes erupted on the border.
The violence comes before the opening of the US embassy in Jerusalem, which has infuriated Palestinians.
They see it as clear US backing for Israeli rule over the whole city, whose eastern part Palestinians lay claim to.
Top US officials, including President Donald Trump’s daughter and her husband, will attend the event.
Gaza’s Islamist rulers, Hamas, have led mass protests in a “Great March of Return” for the past six weeks. Israel says demonstrators are trying to breach the border fence.
Children were among those killed on Monday and more than 1,000 people were injured, the Hamas-run health ministry says.
Palestinians hurled stones and firebombs, while the Israeli military used snipers as black smoke poured from burning tyres.
Israel’s army said 35 000 Palestinians were taking part in “violent riots” along the security fence and that its troops were operating “in accordance with standard procedures”.