President Joe Biden pushed Israeli prime minister Benjamin Netanyahu to take concrete steps to minimize civilian casualties in Gaza in a call between the two leaders on Thursday and urged his counterpart to agree to an “immediate ceasefire” deal with Hamas.

Biden linked continued U.S. support for Israel to Netanyahu’s willingness to take “measurable” steps to reduce civilian casualties after a group of aid workers were killed in an accidental Israeli airstrike while delivering food in Gaza on Monday.

“He made clear the need for Israel to announce and implement a series of specific, concrete, and measurable steps to address civilian harm, humanitarian suffering, and the safety of aid workers,” the White House said in a statement following the call. “He made clear that U.S. policy with respect to Gaza will be determined by our assessment of Israel’s immediate action on these steps.”

“He underscored that an immediate ceasefire is essential to stabilize and improve the humanitarian situation and protect innocent civilians, and he urged the Prime Minister to empower his negotiators to conclude a deal without delay to bring the hostages home,” the statement continued.

Biden and Netanyahu’s call took place days after a strike by Israeli forces killed seven humanitarian aid workers from the World Central Kitchen causing the charity to suspend its Gaza operations. Netanyahu said the strike was not intentional and the Israeli Defense Forces are investigating the matter.