“We must avoid at all costs the resumption of hostilities in Gaza that would lead to an immense tragedy,” Guterres said.
He also called on Hamas to follow through with the scheduled release of hostages next Saturday.
Guterres emphasized the need for “both sides” to uphold the ceasefire and resume “serious negotiations in Doha for the second phase.”
The UN chief’s remarks came amid heightened concerns over the fragile truce, as international mediators work to secure lasting peace in the region.
A three-phase ceasefire has been in effect in Gaza since January 19, pausing Israel’s assault that has killed over 48,000 people and devastated the region.
In the first phase, lasting until early March, 33 Israeli hostages are set to be exchanged for Palestinian prisoners, with the sixth swap planned this week.
In November, the International Criminal Court issued arrest warrants for Israeli Prime Minister Benjamin Netanyahu and former Defense Minister Yoav Gallant over war crimes in Gaza.
US President Donald Trump has warned that the Gaza ceasefire deal should be cancelled if all the Israeli captives are not released by Saturday.
His statement came after Hamas suspended the next release of captives held in Gaza indefinitely, accusing Israel of violating the terms of the ceasefire agreement, including by continuing to kill Palestinians and obstructing the delivery of humanitarian aid.
The moves sparked protests in Tel Aviv, while the Israeli military says it has cancelled leave for its troops and is increasing its forces around the Gaza Strip.
