United Nations Secretary-General Antonio Guterres on Sunday denounced Israel for the "heartbreaking" deaths of Palestinian civilians in Gaza and called it unacceptable to resist statehood for the Palestinian people.

"Israel's military operations have spread mass destruction and killed civilians on a scale unprecedented during my time as secretary-general," Guterres said at the opening of a summit of the G77+China in the Ugandan capital Kampala.

"This is heartbreaking and utterly unacceptable. The Middle East is a tinder-box, we must do all we can to prevent conflict from igniting across the region."

Israel launched its offensive in Gaza after the Oct. 7 Hamas incursion that killed around 1,140 people and 240 taken hostage.

Israel's campaign, on the other hand, has killed more than 25,000 Palestinians, according to Gaza health authorities Sunday, and displaced most of the enclave's 2.3 million people from their homes.

Guterres added that the refusal to accept the two-state solution for Israelis and Palestinians is totally unacceptable, saying denying Palestinians the right to statehood "would indefinitely prolong a conflict that has become a major threat to global peace and security."

Israeli Prime Minister Benjamin Netanyahu appeared on Saturday to push back against U.S. President Joe Biden's remarks about Palestinian statehood after the war on Gaza ends.

His office said that in talks on Friday with Biden, Netanyahu "reiterated his policy that after Hamas is destroyed Israel must retain security control over Gaza to ensure that Gaza will no longer pose a threat to Israel, a requirement that contradicts the demand for Palestinian sovereignty."

Guterres was in Kampala to attend the summits of G77+China and the Non-Aligned Movement (NAM). Leaders and senior officials from dozens of countries including South Africa, Iran, China, Türkiye, Cuba, India, Vietnam and others attended the meetings.

The G77+China is a group of 134 developing countries that champions the common interests of countries from the global south.

A document released late Saturday at the end of the NAM summit included a condemnation of "the illegal Israeli military aggression on the Gaza Strip, the indiscriminate attacks against Palestinian civilians, civilian objects, the forced displacement of the Palestinian population" and called for an immediate and durable humanitarian cease-fire.