Antonio Guterres made the remarks on Saturday, addressing a summit of the Non-Aligned Movement (NAM) in the Ugandan capital of Kampala.
He denounced "the denial of the right to statehood for the Palestinian people" as "unacceptable," asserting, "The right of the Palestinian people to build their own state must be recognized by all."
Refusal to accept the Palestinians' right to statehood, Guterres added, "would indefinitely prolong a conflict that has become a major threat to global peace and security..."
In its final summit communiqué, the Non-Aligned Movement also "strongly condemned the illegal Israeli military aggression against the Gaza Strip," and called for "a lasting humanitarian ceasefire."
The assembled leaders in Kampala also called for "the independence and sovereignty of the State of Palestine" with East al-Quds as its capital.
NAM is a forum of 120 countries that are not formally aligned with any major power bloc.
AMK/PressTV