Gueterres was speaking at the Doha Forum conference as Washington vetoed on Friday a proposed U.N. Security Council demand for an immediate humanitarian cease-fire in the war between Israel and Palestinian militant group Hamas.
"I urged the Security Council to press to avert a humanitarian catastrophe and I reiterated my appeal for a humanitarian cease-fire to be declared," Guterres said.
"Regrettably, the Security Council failed to do it, but that does not make it less necessary," he said.
"I will not give up," Guterres added.
Qatar's Prime Minister Sheikh Mohammed bin Abdulrahman Al Thani told the gathering that Doha will continue to pressure Israel and Hamas for a truce despite "narrowing" chances.
Qatar, where several political leaders of Hamas are based, has been leading negotiations between the group and Israel.
Sheik Mohammed said hostages were released from Gaza because of negotiations and not because of Israel's military actions.
The head of UNRWA, the U.N. aid agency for Palestinians, said the dehumanization of Palestinians has allowed the international community to tolerate Israel's continued attacks on Gaza.
"There is no doubt that a humanitarian cease-fire is needed if we want to put an end to hell on earth right now in Gaza," UNRWA chief Philippe Lazzarini said.
The United States and Israel oppose a cease-fire because they believe it would only benefit Hamas. Washington instead supports pauses in fighting to protect civilians and allow the release of hostages taken by Hamas in a deadly Oct. 7 attack on Israel.
COP28
Guterres also urged leaders at the COP28 climate conference to agree on deep cuts to emissions and stop global warming exceeding 1.5 degrees Celsius (2.7 degrees Fahrenheit).
He said that despite pledges, emissions are at a record high and fossil fuels are the major cause.
Oil producing powers clashed on Saturday with the rest of the countries over a possible agreement to phase-out fossil fuels at the climate summit in Dubai, jeopardizing attempts to deliver a first-ever commitment to eventually end the use of oil and gas in 30 years of global warming talks.
"I urge leaders at COP28 in Dubai to agree on deep cuts to emissions, in line with the 1.5-degree limit," Guterres said adding that fossil fuel companies and their backers should use their enormous resources to lead the renewables revolution.
Forum