Gazans are "in the midst of an epic humanitarian catastrophe before the eyes of the world," UN Secretary-General Antonio Guterres said on Wednesday.
"Intense negotiations are taking place to prolong the truce -– which we strongly welcome -- but we believe we need a true humanitarian ceasefire," he said at a UN Security Council meeting.
A current truce in the Israel-Hamas conflict is scheduled to expire early Thursday after a six-day pause in a conflict sparked by deadly Hamas attacks that prompted a devastating Israeli military offensive in the Gaza Strip.
With 60 Israeli hostages and 180 Palestinian prisoners already released and more set to walk free on Wednesday under the agreement, conflict mediator Qatar said negotiators were working for a "sustainable" ceasefire.
After a 48-hour extension of an initial four-day truce, a new group of 12 hostages -- 10 Israelis plus two Thais -- was freed from Gaza on Tuesday, with 30 Palestinians released by Israel.
"I welcome the arrangement reached by Israel and Hamas -- with the assistance of the governments of Qatar, Egypt and the United States," Guterres said.
The truce has brought a temporary halt to fighting that began on October 7 when Hamas militants poured over the border into Israel, killing 1,200 people, mostly civilians, and kidnapping about 240.
Israel's subsequent air and ground campaign in Gaza has killed nearly 15,000 people, also mostly civilians, according to Hamas officials, and reduced large parts of the north of the territory to rubble.
"Meanwhile, an estimated 45 percent of all homes in Gaza have been damaged or destroyed," Guterres said.