Riyadh, Saudi Arabia - Shi'ite Muslims across the Middle East this week mark the Ashura religious festival, which has been politicised more than usual by sectarian violence in Iraq and Lebanon.
The rites will reflect growing Shi'ite power in the region and fears of clashes are high amid charges by some Sunni clerics that Iran has been promoting missionary activity.
"In the past year the situation in the region and globally has been tense," said Khalil Almarzooq, deputy leader of the Wefaq parliamentary bloc, the largest Shi'ite group in Bahrain.
"And there are attempts from outside and inside to stoke sectarian tension, such as saying Shi'ites are followers of Iran, and this doesn't do anybody any good," he added.
In recent decades, Ashura - with displays of men whipping and cutting themselves to emulate the suffering of the Prophet's grandson Hussein - has been a gauge of the rise in the political power of Lebanon's traditionally poor and marginalised Shi'ites.
During Ashura - the 10th day of the Islamic month of Muharram which falls on Monday or Tuesday - Shi'ites commemorate the slaying of Hussein and his followers at Kerbala, located in modern Iraq, in 680 AD by the army of an Islamic empire based in Damascus.
Shi'ite tradition depicts Hussein and his family as semi-divine "perfect men", as well as the rightful leaders of the Islamic nation through their blood link to the Prophet. This has set them at odds for centuries with the Sunni Muslims, who dominate much of the non-Iranian Middle East.
Hussein's tragic end has often been seen as an inspiration in fights against injustice and suffering, and this has struck a chord with Shi'ites in Iraq, Lebanon, Saudi Arabia and Bahrain who maintain close links with Iran, a non-Arab Shi'ite power.
Sectarian violence has escalated in Iraq since the bombing of a Shi'ite shrine in Samarra in 2006, pushing the country to the brink of a civil war as power has been transferred to the majority Shi'ites from the minority Sunnis under Saddam Hussein.
In Lebanon Shi'ites are leading efforts to bring down the Western-backed government which is supported by Sunni Muslims and some Christians.
IRAQ NOW A SHI'ITE POWER
Although Shi'ites are the minority sect of Islam, they form some 60 percent of Iraq's 26 million people and have dominated the government following the U.S.-led invasion of 2003.
Since the invasion, millions of Shi'ites make the pilgrimage to Hussein's shrine in Kerbala, transforming the Ashura festival into the biggest national day and confirming the ascendancy of Shi'ism.
But 171 Iraqi pilgrims were killed in Ashura attacks in 2004, and security is tight this year to keep out suicide bombers from radical Sunni groups like al Qaeda.
Iraqi Sunnis even say Shi'ites should stay indoors.
"Whoever wants to celebrate should do it within their neighbourhoods or their homes," said Iraqi politician Saleem al-Jubouri. "We don't need more casualties in the current security situation."
In the Gulf, Shi'ites in Saudi Arabia and Bahrain complain of second-class treatment from Sunni authorities and clerics who sometimes look on them as virtual heretics.
Only in Kuwait is sectarian difference a less politically charged issue, since Shi'ites -- who form one third of a 1 million population -- occupy an affluent place in society.
There are thought to be several million Shi'ites in Yemen, and some in the neighbouring Saudi region of Najran, but they are from different sects than those in Iran, Iraq and the Gulf.
In recent weeks, influential Saudi clerics have issued fatwas, or religious decrees, attacking Shi'ites as infidels bent on murdering Sunnis in Iraq in collaboration with non-Arab Iran. "Some of the fatwas ... have the potential to increase tension between the two sects," said Fahad Nazer, a Saudi analyst based in Washington.
A heavy Saudi security presence limits Shi'ite celebrations to Shi'ite-only districts of the Eastern Province on the Gulf coast, where they are thought to number more than 2 million. (Additional reporting by Mohammed Abbas, Aseel Kamy)