Tens of thousands of Palestinians, pressing for a right of return for refugees to what is now Israel, gathered at five locations along the fenced 40-mile frontier where tents were erected for a planned six-week protest, local officials said.
Demonstrators were also seen burning and stamping on posters with the face of U.S. President Donald Trump, who ordered the US embassy in Israel moved from Tel Aviv to Jerusalem. The protesters have vowed to remain at the border until the embassy moves to Jerusalem on May 14.
The Israeli military estimated there were 30,000 demonstrators and used a drone to drop tear gas on the massive crowds.
Gaza health officials said one of the 12 dead was aged 16 and at least 400 people were wounded by live gunfire, while others were struck by rubber bullets or treated for tear gas inhalation.