Muslims across the world celebrated Eid al-Fitr on Sunday marking the end of Ramadan, but authorities urged caution as large social gatherings and returning Mecca pilgrims fuelled fears of swine flu spreading.
In Cairo, where two people have died from the A(H1N1) flu virus and nearly 900 cases of infection have been reported, preachers suggested worshippers perform the traditional Eid dawn prayer at home rather than at crowded mosques.
"We ought to cancel Eid prayers... there should be a national campaign to keep crowded places clean and ensure they are safe for people," Suad Saleh, head of Islamic Jurisprudence at Al-Azhar University told the English-language Egyptian Gazette.
Cairo airport authorities have reinforced swine flu testing measures as the end of Ramadan means the return of thousands of pilgrims from Saudi Arabia.
Fear of the virus spreading in the crowded conditions during the pilgrimage is shared by many other countries who are considering cancelling the annual Hajj pilgrimage this year.
Jordanians have been urged to refrain from kissing each other in a bid to combat the contagious disease.
"People should not kiss at social events and gatherings. Instead, they should just shake hands," the government's fatwa (religious edict) department said in a statement ahead of Eid when families and friends gather in large groups.
In Jakarta, thousands of people lined for hours outside the presidential palace to pay their respects to President Susilo Bambang Yudhoyono, state news agency Antara reported.
Indonesian officials fearful of the spread of swine flu set up thermal scanners at the open house event, which is part of a custom that sees people throughout the country ask for forgiveness from others for slights and offences.
In the world's largest Muslim-majority country, nearly 30 million people were estimated to have emptied out of cities and towns in a yearly exodus to celebrate the holiday but traffic chaos has already claimed 184 lives, transport ministry spokesman Bambang Ervan said.
The start of Eid is traditionally determined by the sighting of the new moon, often dividing rival Islamic countries and sects over the exact date.
In Iraq, Shiites loyal to the Grand Ayatollah Ali Husseini al-Sistani, the nation's top Shiite cleric, continued to fast on Sunday, observing nationally televised and locally delivered messages that the new moon had not yet been observed.
However those who follow the Shiite anti-US cleric Moqtada al-Sadr ended the holy month of Ramadan early Sunday. Iraq's minority Sunnis ended Ramadan on Saturday.
In neighbouring Iran, politics dominated the prayer with supreme leader Ayatollah Ali Khamenei blasting arch-foe Israel, Western powers and foreign media networks in a sermon, saying that a "Zionist cancer" was gnawing into the lives of Islamic nations.
In Afghanistan, President Hamid Karzai extended an olive branch to Taliban militants trying to overthrow his Western-backed government.
"On this auspicious day once again I ask all those Afghan brothers who are unhappy or are in others' hands to stop fighting, destroying their own land and killing their own people," he said.
"They must come to their houses and live in peace in their own country," he said, speaking to reporters at the presidential palace in Kabul.
Pakistani families uprooted by conflict with the Taliban face a miserable Eid, with no cash to splash on celebrations and longing to return to homes they fear no longer exist.
The United Nations said about two million Pakistanis were displaced as a result of fighting between the army and Taliban militants, which the United States branded an existential threat to the nuclear-armed country.
Meanwhile, residents of restive Indian Kashmir jammed markets in defiance of a rise in militant violence to stock up for Eid.
The festival to celebrate the close of the holy month will be held Monday or Tuesday, depending when the new crescent moon is sighted over the region where Islamic militants have been fighting against New Delhi's rule for 20 years.
Shopkeepers set up extra kiosks to cater to the mad shopping rush.
Muslim separatists however, who are spearheading a political movement to break the region away from India and link up with neighbouring Pakistan or make it an independent state, called for austerity.