Ramadan, the Muslim holy month of fasting, will begin on Sunday in Saudi Arabia, the state-run Al-Ekhbariya television channel reported on Friday.
Citing the authorities, it said that because the crescent moon was unable to be seen with the naked eye on Friday, Ramadan would begin on Sunday.
According to tradition, it is the sighting with the naked eye of the new moon that signals the start of Ramadan.
Other Gulf monarchies, including Bahrain, Kuwait, Qatar and the United Arab Emirates also said Ramadan will start in their countries on Sunday.
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Algeria will also mark the start of the holy month on the same day.
Yemen's religious authorities said in a statement that fasting would begin on Saturday.
During Ramadan, Muslim believers abstain from eating, drinking, smoking and having sex from dawn until sunset.
Ramadan is sacred to Muslims because it is during that month that tradition says the Koran was revealed to the Prophet Mohammed.
The fast is one of the five main religious obligations under Islam.