Across the Muslim world, the faithful fast from dawn to dusk and strive to be more pious during the holy month, which ends with the Eid holiday.
Ramadan got under way in Asian countries including Indonesia, which has the world's biggest Muslim population at around 225 million people, war-torn Afghanistan, Malaysia, Sri Lanka and the Philippines.
Hardliners in Indonesia have pledged to raid bars that continue to sell alcohol, which Muslims are banned from drinking under Islamic law, or stay open too late. Authorities order bars and other nightspots to close earlier during the holy month.
"If law enforcement officials do nothing about immoral activities, we will do anything we can to stop them, using our own methods."
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But the threats did little to deter people in the football-crazy nation, where most practise a moderate form of Islam, from heading out to catch the latest World Cup action.
Bars that remained open in Jakarta were packed with locals and expatriates yesterday and early today.
"For me, the fasting does not really affect my enthusiasm to watch the World Cup," said Intania Permata, a 22-year-old student, who was watching the Brazil versus Chile nail-biter at a South American bar and restaurant.