Ramadan begins on Tuesday in Egypt and Lebanon, religious authorities in the two countries announced on Sunday.
"April 13 will be the first day of Ramadan," said Egypt's Dar Al Ifta, the institution that issues religious edicts in the Arab world's most populous country.
In Lebanon, top Sunni Muslim cleric Grand Mufti Sheikh Abdellatif Deryan also confirmed the holy month would begin on Tuesday.
The beginning of Ramadan for Turkey will also take place on Tuesday, according to a statement by the presidency, adding that Eid Al Fitr will be on May 13, "corresponding to the first day of the month of Shawwal for the Hijri year 1442”.
In Jerusalem, the Grand Mufti Sheikh Mohammad Hussein declared the start of Ramadan from Tuesday after gathering religious scholars at Al Aqsa mosque compound, the third holiest site in Islam.
"The sighting of the crescent moon for the month of Ramadan has been proven under Islamic law this evening," he said in a statement published by the Palestinian news agency Wafa.
The start of Ramadan is set by both lunar calculations and sightings of the new moon crescent.
Saudi Arabia, custodian of Islam's two holiest sites, will also observe Ramadan from Tuesday after the new moon was sighted.
The kingdom's Supreme Court on Sunday called on all Muslims in the kingdom to watch for the crescent moon “by naked eyes or through binoculars" and for anyone who sighted it to "report to the nearest court and register his testimony”.
Neighbouring Kuwait also declared the start of Ramadan from Tuesday after the crescent moon was clearly seen on Monday, according to the moon-sighting committee.
Ramadan fasting 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 because of the 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.