Bahrain troops and protesters in standoff near palace

Security forces and pro-government vigilantes carrying clubs and swords faced off against protesters near Bahrain's royal complex today in a showdown that displayed that deepening conflict between Sunni Muslims backing the ruling system and Shiites demanding it give up its hold on power.

Hundreds of pro-reform marchers — some wearing white headbands as a symbol of their willingness to die — stood just 500 metres from the wall of riot police with armoured vehicles and a hundreds-strong Sunni mob armed with street fight-style weapons.

Any incident could further enflame tensions between Bahrain's Sunnis and majority Shiites, who have increasingly called for toppling the Western-allied monarchy in the small but strategic island nation that hosts the US Navy's 5th Fleet.

Even some main opposition parties had urged to cancel the march, fearing Bahrain was moving dangerously close to a full-scale sectarian conflict after nearly a month of political unrest. On Thursday, students clashed at a school and Sunni groups burned a Shiite-owned supermarket and threatened other businesses.

But mostly Shiite youth groups ignored the appeals to call of the protest near the offices and compounds of Bahrain's king and other members of the ruling dynasty that has held power for more than two centuries.

A statement by Bahrain's interior ministry warned against the march amid a "level of sectarian tension that threatens Bahrain's social fabric."

Major Sunni-Shiite clashes occurred during the 1990s and forced Bahrain's Sunni rulers to introduce political reforms that included an elected parliament. But the island's Shiites — about 70 per cent of the population — still see themselves stuck in a permanent underclass status.

They are effectively blackballed from top government or security posts and complain that voting districts are gerrymandered to prevent a Shiite majority in the 40-seat parliament, where the main Shiite bloc took 18 seats in elections last year.

A main grievance is the Sunni naturalization policies, which seek to offset the lopsided Shiite demographic advantage and bulk up the ranks of loyalists. Opposition groups estimate tens of thousands of Sunnis from across the Arab world and South Asia have been brought to Bahrain in recent years.

On Wednesday, thousands of Shiites marched outside the immigration office in the capital Manama to decry the "political naturalizations" and demand a mass expulsion.

Bahrain's leaders, meanwhile, are under strong regional pressure to stand firm.

The other Sunni Arab dynasties in Gulf — particularly Saudi Arabia — fear any crack in Bahrain could encourage more uprisings across the oil-rich region to demand an end to their authoritarian grip. Protests have flared already in Oman and Kuwait. Saudi security forces were out today in a major show of power amid rumblings of wider demonstrations.

The Gulf Sunni leaders also see Bahrain as a potential beachhead for Shiite powerhouse Iran. Although there is no evidence of political ties between Tehran and Bahrain's main Shiite groups, some hard-liners in Iran have called Bahrain the "14th province" of the Islamic Republic.

Yesterday, the six-nation Gulf Cooperation Council backed a $10 billion aid plan for Bahrain and Oman, the relatively poorest nations among the super-wealth bloc.

In Geneva, UN human rights officials said three prominent human rights activists in Bahrain are being targeted by death threats conveyed through Facebook and other social media sites. Rupert Colville of the UN Office of the High Commissioner for Human Rights said the messages on Facebook and other social media Web sites denounce the three men as "traitors" and aim to incite people to kill them.