RAMADI, Iraq (Reuters) - Across Iraq's western desert, thousands of Sunni Muslims block highways, chant and pray in protests against Shi'ite Prime Minister Nuri al-Maliki that grow more defiant by the day.
Their demands are many, but the old Iraqi flags from Saddam Hussein's era and Sunni tribal colors fluttering among them are a clear message to Maliki: Enough, our time has come again.
In Iraqi cities like Ramadi and Falluja, where tribal ties are strong, many Sunnis have harbored a sense of marginalization ever since Saddam's fall and the Shi'ite majority's empowerment.
But the pent-up Sunni anger that erupted a month ago has many worried that Iraq is heading for an explosion of Shi'ite-on-Sunni violence that will divide it along sectarian faultlines.
Already protests are becoming volatile. Iraqi troops shot five people in clashes in Falluja on Friday, illustrating the room for miscalculation with sectarian hardliners and Islamist insurgents trying to steer unrest into crisis.
Just outside Ramadi, Sunni men sleep in tents and pray along a blockaded highway, wrapping themselves in old three-star Iraqi national flags, chanting slogans and waving migwars, the wooden mace that Iraqis used to fight the British in the 1920s.
Defiant banners hung on tents call out: "No to Maliki's Justice" and "I will not leave until I get dignity".
In fiery speeches from clerics and tribal leaders, talk of reforms mixes with calls to topple the Shi'ite-led government and the more radical demand to split away an autonomous Sunni region in Anbar province along Iraq's western flank.
"This is just the culmination of years of injustice against us," said Munim al-Mindeel, a farmer sitting outside a tent decorated with anti-government banners. "Of course this was bound to happen. All pressure brings explosions in the end."
The turmoil has erupted at a risky time. War in next-door Syria, where mostly Sunni rebels are battling President Bashar al-Assad, is feeding the ambitions of Iraqi Islamists eager to see the rise of a Syrian Sunni regime across Anbar's border.
Anbar, a vast desert heartland of mostly Iraqi Sunnis where al Qaeda once fought American forces, makes up a third of Iraq's territory, and adjoins Syria, Saudi Arabia and Jordan.
A year after the last U.S. troops left, the protests are fast evolving into the most dangerous test yet for Maliki and the OPEC country's precarious post-war settlement sharing power among Shi'ites, Sunni Arabs and ethnic Kurds.
Four suicide bombings in recent weeks delivered a reminder of how al Qaeda and Sunni militants want to inflame tensions. Divisions in Sunni ranks between moderates, Islamists and tribal leaders or sheikhs make ending the crisis even more challenging.
"We are in a state of hyper-volatility, even for Iraqi standards, which invites more chances to miscalculate, overreach, overreact," said Ramzy Mardini at Beirut's Iraq Institute for Strategic Studies.
After defeating a vote of no confidence last year, Maliki looked to have shored up his position among the complex alliances of Shi'ite parties, Kurdish parties and the Sunni-backed Iraqiya party, which are all split into rival factions.
But the Sunni protests have opened up another front for the Shi'ite leader just as he struggles with a dispute over oil with the autonomous Kurdistan region.
With provincial elections in April seen as a test for the 2014 parliamentary ballot, politicians across the sectarian and ethnic divides all have scope to put pressure on Maliki, lawmakers say.
Maliki has appointed a top Shi'ite to negotiate, and has freed hundreds of Sunni detainees. But his concessions look to have come too late for protesters who are turning against Sunni politicians seen as having been co-opted by the government, lawmakers and sheikhs say.
In Ramadi, the tribal leaders want reform of laws they see as unfairly targeting Sunnis: Iraq's Antiterrorism law and the Justice and Accountability law, which aims to weed out members of Saddam's outlawed Baath party.
The so-called debaathification is sensitive for both sects: Shi'ite leaders want guarantees that senior supporters of Saddam will not return to power, Sunnis say they are being denied benefits and jobs where former Shi'ite Baathists are left alone.
"What did I do to be deprived of a pension?" said one former Baath party member at the Ramadi protest camp. "Why do I have to be deprived of my dignity for one thing I did?"
Those demands are especially sensitive in Falluja and Ramadi, where tribal leaders took up arms against American troops after the invasion. Sickened by al Qaeda's tactics, they later turned against insurgents to join with U.S. forces.
The Sunni protests erupted in December after authorities arrested the bodyguards of Sunni finance minister Rafaie al-Esawi, a Falluja native, on terrorism charges. It was a move Sunni leaders believe was part of a campaign against their sect.
"We'll have no choice but to ask for a new government if they keep on ignoring us," Sheikh Hameed al-Shook, an Anbar tribal leader, said in his Ramadi compound, fringed by date palms. "Everything indicates the government wants to cancel out the Sunni identity."
Anbar's sheikhs and lawmakers worry that if they are seen to be sidelined, the protests will fall under the control of hardline clerics and Islamists seeking to promote a more radical agenda, including calls for an autonomous Sunni region.
The Iraqi Islamic Party, part of the Muslim Brotherhood, has been a prime mover in a drive to create a Sunni entity along the border with Syria, by force if needed, senior Sunni sources say.
Under the constitution drawn up after the U.S.-led invasion, each province or group of provinces can create a federal region if it wins enough votes in a referendum.
"Radical Islamists want to come to Baghdad, they want to start from scratch, to go back to before 2003," said one Sunni Iraqiya lawmaker.
Al Qaeda's local wing, Islamic State of Iraq, is also regrouping in the deserts of Anbar, and sending some fighters to join Syria's rebels, Iraqi security officials acknowledge.
While moderates called for calm after Friday's deadly clashes, in Falluja, small groups of protesters waved the black jihadist banner of al Qaeda. The group had claimed a suicide bombing that killed a top Falluja lawmaker days earlier.
Maliki, sensitive to Shi'ite worries about former Baathists and Sunni Islamists, warned about protests being hijacked by "remnants of the former regime and al Qaeda and those with a sectarian agenda".
Increasingly, though, for the Shi'ite leadership, Syria's crisis is a key factor in Iraq's own stability.
Should Assad fall it would weaken the sway of Shi'ite Iran, Syria's main regional ally and a key supporter of Shi'ite Islamist parties in Maliki's coalition. Sunni states such as Saudi Arabia, Qatar and Turkey have backed Assad's foes.
After any Syrian collapse, Iraqi Shi'ite officials see Islamist fighters turning their weapons back on Baghdad. Their worst case scenario is a Sunni population in revolt against Baghdad and becoming a magnet for jihadists.
"Everyone is asking where are we heading, no one knows," said one influential Shi'ite leader. "Our biggest fear is that the regime in Syria collapses, then an Iraqi Sunni region will be announced next day, and fighting will erupt."
Additional reporting by Ahmed Rasheed and Suadad al-Salhy; Editing by Kevin Liffey