"The Supreme Court has decided that tomorrow, Thursday, is the completion of the 30th day of the month of Ramadan, and that Friday is the day of the Blessed Eid ul Fitr," the Saudi Press Agency reported.
Meanwhile, the United Arab Emirates (UAE), Bahrain, and other Gulf nations also reported that the Shawwal crescent was not sighted.
Eid ul Fitr, marking the end of Ramadan, is determined by the sighting of the crescent moon according to the Muslim lunar calendar.
Observing the Ramadan fast is one of the five pillars of Islam. Observant Muslims are also encouraged to donate to the poor.
Across the Muslim world, Ramadan festivities this year were overshadowed by the ongoing war in the Middle East, triggered by the US and Israel's attack on Iran.
The Gulf region has been pummelled with repeated strikes by Iran in a retaliatory blitz, with airports, residential areas, energy installations and military bases targeted with ballistic missiles and drones.