Tens of thousands of Palestinians are protesting the opening of the new U.S. Embassy in Jerusalem, and Israeli army forces have killed 55 protesters, according to the Gaza Health Ministry. The ministry also says some 2,770 people have been hurt in demonstrations and clashes.

More than 35,000 people are protesting along the Gaza border, the Israel Defense Forces say. The army says it killed three protesters who were trying to set a bomb next to the security fence in Rafah. It’s the most deaths in one day the area has seen since the summer of 2014, when more than 2,000 Palestinians died.

Palestinian Authority President Mahmoud Abbas called it a “massacre,” and asked for a new partner to step forward and replace the U.S. in brokering talks with Israel.

The White House is blaming the deaths on the Palestinian Islamist group Hamas.

“The responsibility for these tragic deaths rests squarely with Hamas,” principal deputy press secretary Raj Shah said at a White House press conference Monday afternoon.

The number of casualties rose steadily on Monday, as the opening of the American embassy at 4 p.m. local time (9 a.m. ET) neared. The health ministry published a list of the dead, showing that their ages ranged from 14 to 39 years old.