At least 18 Palestinians in Gaza have been shot dead by Israeli troops after bloody clashes erupted on the border, Palestinian officials say.
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.
A 14-year-old boy was among those killed on Monday and more than 900 people were injured, the Hamas-run health ministry said.
Palestinians hurled stones while the Israeli military used snipers as black smoke poured from burning tyres.
Israel's army said 10,000 "violent rioters" had gathered along the security fence and that its troops were operating "in accordance with standard procedures".
Demonstrations are planned across the Palestinian territories to protest the U.S. decision to shift its embassy from Tel Aviv to Jerusalem and recognize the city as Israel’s capital, seen as a major blow to the Palestinian cause.
But they are expected to be largest in Gaza, where six weeks of demonstrations dubbed the “March of Return†will reach a climax this week. Before Monday, Israeli snipers already killed nearly 50 Palestinians in the unrest at the fence, according to the Gaza Health Ministry, and shot 2,240 more.