"Every year, I express my best wishes for Eid al-Fitr to the Muslim community around the world," Guterres said in his Eid message on X.
"My heart is broken knowing that in Gaza, Sudan and many other places -- because of conflict and hunger -- so many Muslims will not be able to celebrate properly," Anadolu Agency reported Guterres added.
Sudan has been ravaged by clashes between the army and the paramilitary Rapid Support Forces (RSF) since April last year. More than 13,000 people have been killed and over 8 million have been displaced according to the UN, while half the population, or 25 million people, are in need of humanitarian assistance.
Israel has killed more than 33,000 Palestinians since an Oct 7.
Much of Gaza's infrastructure has since been destroyed and 1.9 million residents forcibly displaced, leaving them at risk of disease and famine.
-- BERNAMA