"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 United Nations Security Council meeting.
Palestinian Foreign Minister Riyad al-Maliki told the meeting that the Palestinian people "are faced with an existential threat" amid the conflict.
"We are owed respect to our inherent dignity... Israel has no right to self-defense against a people that it occupies," he said.
The ongoing truce in the latest conflict between Israel and Hamas is scheduled to expire early Thursday after a six-day pause in the fighting, which was sparked by deadly Hamas attacks on October 7 that prompted a devastating Israeli military offensive in the Gaza Strip in return.
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.
Israel's ambassador to the UN Gilad Erdan said that "anyone who supports a ceasefire basically supports Hamas's continued reign of terror in Gaza."
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 the fighting that began last month 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.
