Two prominent Democratic senators urged President Joe Biden to take immediate action to help negotiate an urgent cease-fire after more than 100 people were killed when Israeli troops opened fire on a crowd waiting for humanitarian aid in Gaza City on Thursday.

Sens. Chris Murphy (D-Conn.) and Chris Van Hollen (D-Md.), who both sit on the powerful Senate Foreign Relations Committee, said the White House must demand accountability after the mass deaths and ensure aid can reach those starving in Gaza as soon as possible.

“People are starving in Gaza. And civilians are dying every day — including in this horrific incident in Gaza City today,” Van Hollen said in a statement. “This has gone on for far too long without sufficient action.”

Gaza officials and Israel have traded blame for the death toll.

The Gaza Health Ministry said Israeli forces opened fire on a crowd gathered near a convoy of aid trucks on Thursday. Officials described the gunfire as a “massacre,” saying more than 100 had died and more than 760 were injured as desperate Palestinians struggled to get food. It was the first major aid delivery to the area in a month.

Israel admitted that its troops had fired warning shots but claimed troops fired only on people who approached the trucks in a threatening way. Israel instead attributed many of the deaths to a stampede.

“We didn’t open fire on those seeking aid,” the chief military spokesperson for the Israel Defense Forces told The Associated Press. “Contrary to the accusations, we didn’t open fire on a humanitarian aid convoy, not from the air and not from land. We secured it so it could reach northern Gaza.”

The episode quickly prompted international condemnation. Biden said Thursday that any negotiations for a cease-fire will be further complicated, expanding his timeline for any eventual deal. And State Department officials said they were looking into “exactly what took place” in Gaza.

But the senators on Thursday urged the White House to act with haste after the mass deaths.

Murphy added that the deaths Thursday were the result of “the complete breakdown in social order in Gaza,” saying the situation was “spiraling out of control” without humanitarian aid and a negotiated cease-fire.

“To be clear, Hamas started this war and could end it tomorrow by releasing the hostages and surrendering those responsible for the October 7th attacks,” Murphy said. “However, the appalling scenes from Gaza City today and the staggering civilian death toll that has already occurred in Gaza are not in Israel’s nor the United States’ interest.”

Murphy said Biden should use “all available leverage” to see Israel and Hamas reach a longer-term cease-fire.

Van Hollen added Thursday that “enough is enough.”

“America cannot be complicit in this ongoing humanitarian catastrophe,” he wrote. “We know what must be done, now we must do it.”