The body of Israeli hostage Shiri Bibas was not among the four returned by Hamas from Gaza on Thursday, Israel’s military has said, accusing the Palestinian militant group of a “violation of utmost severity” of the precarious ceasefire deal.

Israeli Prime Minister Benjamin Netanyahu vowed revenge Friday for what he described as a “cruel and malicious violation” of the ceasefire agreement.

Famine has been mostly averted in Gaza as a surge of aid enters the territory during a fragile ceasefire, the United Nations humanitarian chief said Sunday. But he warned the threat could return quickly if the truce collapses.