Syrian state television announced that Ramadan would begin on Saturday, but the opposition Syrian National Council and rebels decided to begin a day earlier, in line with many Arab nations.
"The Syrian National Council announces ... Friday is the first day of Ramadan, unlike what was declared by the regime," a SNC statement said.
"According to the trusted bodies of religious scholars in Syria, Friday is the first day of the month of Ramadan," it said.
"As we approach the achievement of the brilliant victory against the tyrannical and corrupt gang, we call on our people to step our their resistance and their opposition to elements of the regime and its militias, and to support the brave brigades in Damascus and their work," it added. Muslim scholars announce the beginning of Ramadan based on their observations of the new moon with the naked eye.
Authorities in Saudi Arabia announced the fasting month would begin on Friday, with Lebanon, Qatar, the United Arab Emirates, Yemen, Kuwait, Jordan, Egypt, Tunisia and Algeria doing the same. But religious authorities in Oman decided that the month would begin on Saturday after failing to spot the new moon.
Iran, Iraq and Lebanon's Shiite community will also begin their fast on Saturday. During Ramadan, Muslims fast from dawn to dusk and strive to be more pious and charitable.