More than two million Muslims from around the world have begun the annual pilgrimage or Hajj in Saudi Arabia, under heavy security.

The pilgrims, in white robes symbolizing purity, traveled Thursday from Mecca to a tent city in the valley of Mina, marking the start of the grueling five-day ritual.

On Friday, the pilgrims will move to nearby Mount Arafat for a day of prayer before Saturday's ceremony symbolizing the stoning of the devil.

Last January, at the stoning ceremony on the Jamarat bridge, more than 360 worshippers died in a stampede.

Saudi authorities have spent more than $1 billion renovating the site to make it safe.

Thousands of police are deployed along the route that traces the prophet Muhammad's journey some 14,00 years ago.

The official Saudi Press Agency says the Hajj has begun smoothly with no major incidents.

The pilgrimage comes at a time of tension between Shi'ite and Sunni Muslims.

The Saudis have banned political protests, but Iranian Shi'ite pilgrims traditionally hold a political rally during the Hajj..

The Hajj is one of the five pillars (obligations) of Islam. Every Muslim who is able to make the voyage is required to do Hajj at least once.

Some information for this report was provided by AFP, AP and Reuters.