Hajj Pilgrims Stone Devil Friday in Annual Hajj Ritual བོད་སྐད།

Hundreds of thousands of Muslim pilgrims performed the ritual "stoning of the devil" Friday outside the Saudi holy city of Mecca, in one of the high points of the annual Hajj.

The ritual coincides with the start of Eid al-Adha, or "Festival of Sacrifice," considered one of the most important days on the Islamic calendar.

The religious feast commemorates the belief shared by Muslims, Christians and Jews that God gave the prophet Abraham a ram to stop Abraham's impending sacrifice of his son.

Sheikh Osman Khayat delivered a sermon before thousands of pilgrims at Mecca's Grand Mosque. He called for unity among Muslims and he condemned divisions he says are provoked by enemy forces.

Security was tight. Saudi authorities deployed thousands of tanks, helicopters, armored personnel carriers and other vehicles to maintain the peace.

This portion of the Hajj has historically been the most dangerous. There have been deadly stampedes in recent years at Jamarat Bridge, where the stoning ritual takes place. In the most severe incident, 365 people died in 2006.

Some 2.5 million people from 160 countries are taking part in the Hajj.

On Wednesday, heavy rains and flooding in Saudi Arabia killed at least 83 people, and stranded hundreds trying to make their way from the port city of Jeddah to Mecca.

Four pilgrims have died from A-H1N1 swine flu since arriving in Saudi Arabia. The Saudi health minister says 67 others have been diagnosed with the virus.

The Hajj is one of Islam's five obligations, or pillars. Every Muslim, if able, must perform it at least once during his or her lifetime.