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Muslim pilgrims circle the Kaaba as pray inside the Grand mosque in the holy city of Mecca, Saudi Arabia, Tuesday, Oct. 23, 2012. The annual Islamic pilgrimage draws three million visitors each year, making it the largest yearly gathering of people in the world. (AP Photo/Hassan Ammar)

Next month, Muslims from around the world will gather in Saudi Arabia for the hajj, an annual pilgrimage to the holy city of Mecca.

The journey will center on celebrating the religion of Islam and personal devotion, but, as a letter sent last week from Muslim-American groups to Secretary of State John Kerry and the State Department illustrates, it will also require participants to navigate at-times dangerous intra-religious tensions.

The hajj, one of the Five Pillars of Islam, is required to be completed at least once by all Muslims, although exceptions are made for people limited either physically or financially, Pew Research Center explained. Pew's fact sheet noted that "more than 3 million people performed the hajj in 2012," 55 percent of whom came from outside of Saudi Arabia.

Participants' varied cultural backgrounds can lead to misunderstandings or even violence during the pilgrimage, as a 2013 incident between American and Australian Muslims demonstrated. Muslim pilgrims from Detroit were "attacked and threatened with death … by a group of Sunni (Muslim) men from Australia because (the American Muslims were) Shias, a minority sect within Islam," USA Today reported at the time.

The recent letter to Kerry mentioned the episode, asking the State Department to ensure that American Muslims would be protected from future violence. Twenty-eight Islamic groups co-signed the letter, sharing their conviction that "every American citizen traveling or living abroad should have the full assurance that the U.S. government will come vigorously to his or her defense if they are unjustly detained, attacked or harassed by local authorities."

In its coverage of the letter, Think Progress reported that the U.S. government is limited in what it can do to ensure the safety of American pilgrims. "Short of sending armed escorts, the State Department is ultimately required to ... respect the autonomy of Saudi Arabia— an American ally— and trust that their officials will keep U.S. citizens safe," Think Progress explained.

However, the article noted that American Muslims aren't likely to be comforted by the promise of Saudi Arabian protection. The State Department's annual report on religious freedom, released in July, "specifically mentioned Saudi Arabia's failure to protect its Shia Muslim minority from religious persecution."

Sunnis and Shias are the two main branches of Islam, varying in their approach to scriptural interpretation and religious authority, Pew Research reported in a 2012 study.

The Pew report concluded that although "sectarian identities, especially the distinction between Sunni and Shia Muslims, seem to be unfamiliar or unimportant to many Muslims," the distinction was shown to be most important to Muslims in Southeast Asia, the Middle East, North Africa and South Asia — the areas surrounding Mecca in Saudi Arabia.

These regional differences further complicate an already challenging hajj observance. Pilgrims risk their health and financial stability, and must also watch out for disasters like stampedes. "The huge gathering holds inherent risks, despite high-tech Saudi crowd control and anti-terrorism efforts," Religion News Service reported.

The U.S. government's initial response to the letter, and to the potential for increased tension at the hajj due to current conflicts in the Middle East, has been a promise to take all threats seriously and to ask American pilgrims to register their location with the State Department, RNS reported.

Email: kdallas@deseretnews.com Twitter: @kelsey_dallas