Religious authorities in most Middle Eastern countries declared that Friday will be the start of the holy month of Ramadan, a period devoted to dawn-to-dusk fasting, prayers and good deeds.

Official statements issued Thursday in Egypt, Saudi Arabia, Lebanon, Jordan, Qatar, Libya and Yemen said the holy month will start the following day.

Political differences and religious disputes between Sunni- and Shiite-majority countries in the region have often played a role in different starting dates for the holy month which is usually calculated based on the sighting of a new moon.

Highlighting the turmoil in Syria, Syria’s government said the holy month will begin Saturday — in contrast to the opposition Syrian National Council, which said it is to be observed starting Friday. On the group’s Facebook page, the SNC urged unity and cooperation among Syrians as they fight Bashar Assad’s regime.

“As we near victory against the gang of repression and corruption, we call on our people to escalate their resistance and confrontation with the regime members and their militia, and to support the heroic brigades in Damascus,’’ the group said. “The holy month of Ramadan will be the month of victory against the criminals.’’

An unprecedented attack on Syria’s National Security building in Damascus Wednesday killed three of Assad’s top lieutenants. Coupled with the rebels’ seizure of two Syrian border crossings, the development suggests an unraveling of Assad’s grip on power after 16 months of violence.

The sighting of the new moon marks the beginning of the Muslim lunar month that varies between 29 and 30 days.

Some countries use astronomical calculations and observatories, while others rely on the naked eye alone, leading sometimes to different starting times in the Middle East. Ramadan begins around 11 days earlier each year.