Jakarta - Millions of Muslims in Indonesia - the world's most populous Muslim country - on Monday begin fasting for the holy month of Ramadan, local media reported.

The Ministry of Religious Affairs announced the government's decision on Sunday evening that Monday is start of the fasting month of Ramadan after a meeting with leaders of Islamic organizations in the country, including the two largest ones, the Nahdlatul Ulama (NU) and Muhammadiyah.

But at least two small groups of Muslims in east Java district of Jember and in Gowa of South Sulawesi, began their fast on Sunday, The Jakarta Post reported.

In most years, Muslims in Indonesia start fasting on different days according to their own lunar observations.

Religious Minister Maftuh Basyuni said that based on data from 27 monitoring posts across the country, only four reported to have seen a small crescent of the moon, while the majority of the posts, due to bad weather, said they had difficulty to see hilal (the moon), which marks the start of the month in the Islamic lunar calendar.

"Based on their reports, it was agreed that the first day of Ramadan this year fell on Monday (September 1)," the state-run Antara news agency quoted Basyuni as saying after chairing the meeting to determine the start of Ramadan, which was also attended by ambassadors from Muslim nations.

Muhammadiyah, the country's second largest Muslim organization, relies on astronomical calculation to determine the start of the holy month, while Nahdlatul Ulama, which claims to have 40 million followers, uses the sighting to the new moon, called rukyah.

During the holy month, Muslims abstain from food and drink from sunrise to sunset, in accordance with one of the five pillars of their religion. The daily fast is broken by prayers and festive meals.

Ramadan is the ninth month in the lunar calendar, when the Islamic holy book, the Koran, was first revealed to the Prophet Mohammed.

Nearly 88 per cent of Indonesia's 230 million people adhere to Islam, making it the world's most populous Muslim nation. (dpa)