The Supreme Court of Saudi Arabia has asked its citizens to keep an eye out for the crescent moon on Tuesday, which, if sighted, will mark the beginning of the month of Ramadan on Wednesday.
If the Ramadan moon is not sighted on Tuesday, the month of fasting will begin on Thursday.
Saudi Arabia has called on Muslims to immediately report the sighting of the crescent moon with a court or an authority, Arab News reported.
The United Arab Emirates (UAE) has also set up a moon-sighting committee, and has asked sharia courts across the country to report sighting of the moon, Emirates 24/7 News reported.
Muslims all over the world will observe a month of fasting and prayers during Ramadan, which is considered to be one of the Five Pillars of Islam.
Ramadan is the ninth month of the Islamic lunar calendar, and commemorates the time that the Quran was revealed to Prophet Mohammed on the night of "Laylat Al Qadr".
Muslims fast from dawn to dusk every day, and also observe sexual abstinence.