Saudi Arabia has mobilised a force of 100,000 men to protect an estimated two million Muslim pilgrims starting the annual hajj on Saturday, amid fears of attack or deadly stampedes.

The interior ministry said that in addition to many thousands of Saudis, an estimated 1.7 million of the faithful have descended on the kingdom from abroad to perform the annual rites.

Local press reports spoke of a throng that could reach three million, and the official SPA news agency reported on Saturday that everything was proceeding smoothly.

The hajj is one of the five pillars of Islam which the Koran says all Muslims must carry out at least once in their lives, if they are able to do so.

It began early on Saturday as pilgrims arrived on foot or by bus in Mina, a dusty valley 10 kilometres (six miles) from the holy city of Mecca.