Saudi Arabia's moon sighting committee had announced that day that the month of Ramadan would begin on Tuesday.
"Tomorrow, Tuesday... is the beginning of the blessed month of Ramadan this year," the kingdom's supreme court said in a royal court statement.
Other Muslim countries, including Sunni-majority Egypt and Lebanon, have also announced that Tuesday marks the start of Ramadan, while Shiite-majority countries like Iran are expected to start a day later.
The daytime fasting month of Ramadan is one of the five pillars of Islam.
Observant Muslims refrain from eating and drinking from dawn to dusk, and traditionally gather with family and friends to break their fast in the evening.
It is also a time of prayers, during which Muslims typically converge in large numbers at mosques, especially at night.
But due to Covid-19 pandemic, many Muslim-majority countries have imposed restrictions on worshippers, including night-time curfews, and called for prayers to be performed at home.
"The month of Ramadan is upon us and the world is suffering from the coronavirus pandemic," Saudi King Salman said in a statement released by state television.
"We thank God for the scientific efforts in developing vaccines to curb the pandemic."
Usually, Kaaba is packed with worshippers throughout the holy month but numbers were limited on Monday due to strict coronavirus precautions.
The Kaaba is a place of pilgrimage that able-bodied Muslims are required to visit at least once in their lives.
Millions of people visit it every year, most of them from abroad.Follow us on Facebook, Twitter and Instagram to stay connected