President Joe Biden told Israeli Prime Minister Benjamin Netanyahu in a phone call on Thursday to implement “specific, concrete, and measurable steps” to curb civilian casualties after the Israel Defense Forces bombed a humanitarian convoy.

Thursday’s call marks the first time the two leaders have spoken since an IDF airstrike destroyed multiple, marked World Central Kitchen vehicles Sunday night, killing at least seven aid workers, including one American citizen, in the process. Israel accepted responsibility for the strike but insists it was an accident.

Biden had previously told WCK founder Chef Jose Andres that the attack left him “heartbroken” and that he would press Israel to change its military operations in Gaza to limit civilian casualties.

“President Biden emphasized that the strikes on humanitarian workers and the overall humanitarian situation are unacceptable. 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‘s readout of the call states. “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.”

White House officials also said that Biden and Netanyahu discussed threats posed by Iran and the U.S. commitment to help Israel defend itself from those threats. The call reportedly lasted roughly half an hour.

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The president has been under increasing pressure as civilian casualties in Gaza continue to mount. Biden hosted Muslim American leaders at the White House on Tuesday for a closed-door discussion on the situation in Gaza, yet White House officials declined to say if they believed the discussion was a success on Wednesday.