The Muslim holy month of Ramadan has begun in most of the Arab world after a new crescent moon was sighted at dusk on Monday.
Lebanon is gearing up for a month of fasting and feasting
However scholars in Oman were unable to see the moon and will join Iraqi Shia in beginning Ramadan on Wednesday.
Sunni and Shia Iraqis have been divided on the issue for three years, ever since the overthrow of Saddam Hussein.
Muslims are meant to fast from dawn to dusk during the coming lunar month, a time of reflection and celebration.
Saudi Arabia, which is home to Islam's holiest sites, announced on Monday on state television that "the crescent moon has been sighted this evening... so tomorrow will be the first day of the holy month of Ramadan".
Similar announcements were made by religious authorities in Algeria, Bahrain, Egypt, Jordan, Kuwait, Lebanon, Libya, the Palestinian territories, Qatar, Sudan, Syria, the UAE and Yemen.
In France, home to Europe's largest Muslim minority, French Muslims have also begun the holy fasting month on Tuesday, although they usually start a day after the Middle East, in line with North African countries.
Oman's state news agency ONA, however, said "the crescent of the holy month of Ramadan has not been sighted".
Indonesia, will also begin fasting on Wednesday. But the sacred season comes at a difficult time for the world's largest Muslim population.
Another suicide bombing in Bali, bird flu worries, and a sharp rise in fuel prices mean Muslims are "facing fasting with a feeling of depression and sadness", according to Ichwan Sam, secretary general of the Indonesian Council of Ulema.
Security has been stepped up in Egypt and Saudi Arabia because of the possibility that militant Muslims will use the festival to launch attacks.
Meanwhile, the Iraqi branch of the al-Qaeda network has called on Sunni Muslims to escalate attacks on US troops in the country during the month.
It is a time of high tension in Lebanon, scene of several bombings this year, as a UN investigation team prepares to publish its findings into the assassination of former Prime Minister Rafik Hariri.
Nevertheless, correspondents say Beirut's bustling pavement cafes, restaurants and downtown boutiques are packed with locals and Arab tourists, who come to dine, smoke water pipes or just stroll through the district.