Nearly 3 million Muslims from around the world, chanting "I am here, Lord" and raising their hands to heaven, marched through a desert valley outside Mecca on Thursday in the first day of the annual hajj pilgrimage. Dressed in seamless white robes symbolizing the equality of mankind under God, the pilgrims hiked through the 13-kilometer (8 miles) valley to Mina, starting a series of rituals in which they cleanse themselves of sin. This year's hajj takes place amid increasing worries across the Islamic world - over the bloodshed in Iraq, violence in the Palestinian territories and a new war in Somalia. Amid the crises, tensions have increased between the two main sects of Islam, Sunnis and Shi'ites, who come together in the five days of hajj rituals centered around the holy city of Mecca, birthplace of Islam's Prophet Muhammad. "We will not allow sectarian tensions from any party during the hajj season," Saudi Arabia's Interior Minister Prince Nayef bin Abdulaziz told reporters ahead of the rituals. "The pilgrimage is not a place for raising political banners ... or slogans that divide Muslims, whom God has ordered to be unified," Saudi Islamic Affairs Minister Sheik Salih bin Abdulaziz told pilgrims Thursday. "The hajj is a school for teaching unity, mercy and cooperation." For pilgrims streaming in from all continents, the hajj is a crowning moment of faith, a duty for all able-bodied Muslims to carry out at least once. On Thursday morning, as they have for the past few days, hundreds of thousands opened their pilgrimage by circling the Kaaba, the black cubic stone in Mecca, Islam's holiest site, which Muslims face when they perform their daily prayers. "For us it is a vacation away from work and daily life to renew yourself spiritually," said Ahmed Karkoutly, an American doctor from Brownsville, Texas. "You feel you part of a universe fulfilling God's will. It's a cosmic motion, orbiting the Kaaba." On Wednesday, massive crowds of pilgrims packed the streets surrounding the Kaaba, some prostrating in prayer, others diving into the traditional outdoor markets to buy perfumes, fabrics, prayer beads and other souvenirs. In gleaming shopping malls overlooking the Kaaba, pilgrims checked out the goods at stores like the Body Shop or lined up at a Cinnabon. "Please do not sit in walkways to allow your brother pilgrims to move freely," announcements in Arabic and English came over loudspeakers as families lay out blankets and sat on pavements outside the Kaaba. Along one curb sat a group of Nigerian women, their robes printed with the name of a charity organization that helped them make the pilgrimage, while nearby were dozens of Afghan women, with bright red ribbons tied to their headscarves to mark their tour group. Saudi authorities estimate nearly 3 million pilgrims are attending this year's hajj - more than 1.6 million from abroad, with the rest Saudis or other residents of the kingdom. More than 30,000 police and other security forces have fanned out around the holy sites to help smooth traffic around ritual sites that have been plagued with deadly stampedes. More than 360 people were killed during last year's hajj in a stampede at Mina during a ritual symbolizing the stoning of the devil, sparked when some pilgrims in the crowd stumbled over luggage. Saudi Arabia spent more than $1 billion over the past year on a project to renovate the stoning site, where the massive crowds of pilgrims file past three stone walls symbolizing the devil to pelt them with stones. New entrances and exits were added around the walls to ease the flow of traffic, and this year authorities made repeated announcements to pilgrims not to bring luggage to the site. On Thursday, the crowds filtered out of Mecca toward Mina through the desert valley, chanting, "Labbeik, allahum, labbeik," Arabic for "I am here, Lord." They will spend the night in a tent city in Mina before heading Friday for Mount Arafat, the site where Muhammad gave his final sermon in 632. There they spend the day and night in prayer and meditation before returning the Mina for the stoning ritual.