Shi'ites and Sunnis divided since death of prophet

The ancient split that divided the Muslim world into Shi'ites and Sunnis began with the death of the prophet Mohammed 14 centuries ago.

Shi ' ites believe that Mohammed's son-in-law Ali was the prophet's true heir and say that all true Islamic leaders must be his descendants.

Sunnis hold that the prophet's rightful successors were the first four caliphs - supreme religious leaders - who are similar to popes. The rivalry between the two branches erupted into open warfare by the end of the 7th century. This ended in a historic battle outside Karbala that saw Ali's son Hussein defeated and killed by a Sunni army.

The two branches of Islam have slight variations in their prayer services and other rituals. Shi'ites believe their religious leaders, as direct descendants of Mohammed, are infallible and without sin.

They depend on religious scholars to interpret Allah's will on major issues, issuing rulings (fatwa). The Sunni faith is less structured.

Two shrines, one to Ali in Najaf and the other for his son, in Karbala, are the most holy sites for Shi'ites.

Thousands of pilgrims flock to the Shrine of Ali to remember Hussein's death each year in bloody rituals that involve pilgrims flaying themselves with whips.

A senior Shi'ite cleric, Ayatollah Muhammad Baqir Al-Hakim, was killed in a car bomb at the shrine last year along with dozens of his followers-Although Shi'ites make up less than 15 per cent of the world's one billion Muslims, they form about 65 per cent of Iraq's population, but were repressed by Saddam Hussein, a Sunni.

The risk of a civil war erupting between the two factions is one of the major concerns for the American administration. But they now fear that the current Shi'ite uprising, led by the radical cleric Moqtada al-Sadr, could unite both groups.

Outside Iraq, Shi'ites are concentrated in neighbouring Iran - the first country to have an Islamic revolution - and Lebanon.

Sunnis are found in north Africa, most of Asia, including Afghanistan, and Saudi Arabia.

Like Saddam, Osama bin Laden is a Sunni.