Women protesting against vice during Ramadan
The highest Muslim authority in Indonesia, the Council of Ulemas, has called for all entertainment venues to be closed during Ramadan.
But in Jakarta the city governor is allowing restaurants and live music halls to operate for reduced hours - except for the six days considered most holy - though it has ordered the closure of all nightclubs and bars.
The Jakarta decree did not explicitly ban alcohol, reported the French news agency AFP.
Muslims must refrain from eating, drinking, smoking and sex each day from dawn to dusk during Ramadan.
Disagreement
There is confusion however over whether the holy month starts on Friday or Saturday.
The government announced late on Thursday that Ramadan would start on Saturday. The previous day the religious affairs minister had reportedly said it would begin on Friday.
The start of Ramadan, the ninth month in the Islamic lunar calendar, is determined either by the sighting of the new moon or through astronomical calculations.
Several Islamic groups and the religious affairs ministry said the new moon was not sighted on Thursday evening and therefore Ramadan starts on Saturday.
Other groups use astronomical calculations, and still say Ramadan started on Friday in Indonesia.
Threats
The president of the Council of Ulemas, Dien Syamsuddin, told the BBC that his group would not tolerate violent action and it was up to the government to implement law and order.
Muhammad Riziq Shihab, chairman of the Front for the Defenders of Islam (FPI), said his group had printed 200,000 stickers which read: "Burn any vicious places that open during Ramadan."
The British embassy in Jakarta warned UK citizens to take special care during Ramadan.
The FPI have recently threatened to "sweep" for foreigners in protest at US-led attacks on Afghanistan.
The group, which the BBC's Richard Galpin says has a reputation for attacking bars and nightclubs, has demanded an end to diplomatic relations with Washington over the military action.