U.S. President Joe Biden says he's "very concerned" that the violence in the Middle East could escalate, adding that the killing of a top Hamas leader in Iran has "not helped" efforts to negotiate a cease-fire in the Israel-Hamas war.

Biden said he'd had a "very direct" conversation with Israeli Prime Minister Benjamin Netanyahu on Thursday. "We have the basis for a cease-fire. He should move on it and they should move on it now."

Netanyahu has said his country was determined to win nothing less than "total victory" against Hamas. He also said that Israel hoped for a cease-fire soon and was working for one.

The assassinations of Hamas leader Ismail Haniyeh in Tehran on Wednesday and senior Hezbollah commander Fouad Shukur in Beirut on Tuesday risks escalating the fighting into an all-out regional war, with Iran also threatening to respond after the attack on its territory. Israel has vowed to kill Hamas leaders over the group's Oct. 7 attack on Israel that sparked the war.

U.S. Secretary of State Antony Blinken was among the growing voices internationally calling for a cease-fire in recent days, saying that it was the only way to begin to break the cycle of violence and suffering.