Millions of Muslims mark start of Ramadan on Monday
The announcement was made on Sunday after the sighting of the crescent moon.
The new moon of Ramadan was spotted on Sunday evening, Saudi Arabia's state TV announced.
Muslims follow a lunar calendar and a moon-sighting methodology that can lead to different countries declaring the start of Ramadan a day or two apart.
Local media in Indonesia, the world's most populous Muslim country, also said Muslims there would begin fasting on Monday, as will Muslims in Singapore, Lebanon, Syria, Qatar, Kuwait, Jordan, Egypt, Afghanistan and Palestine among others.
Following these announcements, a mosque in Tampa, Florida, declared to its followers that they too would celebrate the first day's fasting on Monday.
Other Muslim countries in the Middle East and North Africa are also expected to begin observing Ramadan on Monday or Tuesday.
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During Ramadan, Muslims around the world abstain from eating, drinking and smoking from sunrise to sunset, with exceptions to fasting for children, the elderly, the sick, women who are pregnant, nursing or menstruating, and people travelling.
Many break their fast as the Prophet Muhammad did around 1,400 years ago, with a sip of water and some dates at sunset followed by prayer.
The fast is intended to bring the faithful closer to God and to remind them of the suffering of those less fortunate.
Fasting during Ramadan is one of the five pillars of Islam, along with the Muslim declaration of faith, daily prayer, charity and performing the hajj pilgrimage in Mecca.
It is generally considered against custom for non-Muslims or adult Muslims not observing the fast to eat in public during the day in Ramadan in Muslim-majority countries.
States such as Saudi Arabia, Qatar and the UAE, which are home to large western expatriate communities, have even passed laws against it.
Muslims celebrate the end of Ramadan with a three-day holiday named Eid al-Fitr.
Agencies contributed to this report.