* Raid on Sunni protest camp ignites sectarian clashes
* Sunnis angered by Shi'ite power but split among themselves
* Shi'ites and Kurds seek to revive old pre-Saddam alliance
Wearing military fatigues with his cleric's turban, Sheikh Ali Muhaibes brought Friday prayers in Iraq's Sunni Muslim heartland to a climax with chilling words for the Shi'ite-led government.
"If you want jihad, we're ready. If you want confrontation, we're ready. And if you want us to go to Baghdad, we're coming," he roared to the crowd in the western province of Anbar.
For months, Sunnis have been protesting against Shi'ite Prime Minister Nuri al-Maliki, whom they accuse of marginalising their minority sect and monopolising power since U.S.-led troops toppled Saddam Hussein in 2003. Now the mood is suddenly uglier.
Government concessions had begun to defuse Sunni unrest, but, when security forces raided a protest camp in the town of Hawija on April 23, clashes swiftly spread to other Sunni areas, raising fears that Iraq might slide back into the kind of all-out sectarian bloodletting that ravaged it in 2006-7.
"We worked together to bury sectarianism, but it is rearing its head again," Maliki told Sunni and Shi'ite clerics at an Islamic "rapprochement and dialogue" conference on Saturday.
But many Iraqis fear such efforts will prove futile.
War fatigue may be wearing off, U.S troops who once acted as a buffer are long gone and the war in neighbouring Syria is fuelling Sunni-Shi'ite rivalry across the Middle East.
Protest leaders in Anbar have urged Sunni tribes to provide 100 armed men each for a self-defence "army" for the province.
"We do not accept to live as second-class citizens. We are the sons of Iraq," said Sheikh Abdul-Rahman al-Zubaie, a tribal leader in Ramadi, the provincial capital.
"We have rights ... and when the government denies them, the only way to prove our dignity is through the barrel of a gun."
High-school teacher Mustafa, 28, used to visit the protest camp only on Fridays. Then, he says, the army killed his father and now he goes after class every day, eager for revenge.
His story reflects a wider recrudescence of sectarian hatred in a country still searching for a stable compromise among Sunnis, Shi'ites and ethnic Kurds in the post-Saddam era.
"Iraqi politics may be on the verge of relapsing into a period of sectarian violence, where a new power-sharing deal between the parties is likely needed to reset communal relations," said Ramzy Mardini at the Beirut-based Iraq Institute for Strategic Studies.
"There is an intensity in sentiment and rhetoric that remained dormant for years, but whose undercurrents are surfacing and seeping into discourse and behavior," he said.
"RIVER OF BLOOD"
The April fighting pushed the monthly civilian death count to about 547, according to provisional figures from the Iraq Body Count monitoring group - the highest since 2009, but still well below 2006-7, when the monthly toll sometimes topped 3,000.
Sectarian tensions have also heightened friction among Sunnis divided over what they want and how to achieve it.
Sunni demands range from amending allegedly discriminatory laws to tearing up the constitution and creating an autonomous region like the Kurdish one in the north, by force if need be.
Many tribal leaders have little appetite for more violence, criticising militants for infiltrating the protest movement.
One influential chief in Ramadi, who asked not to be named, said a force was being prepared to confront those he said were seeking to plunge Anbar province into "a river of blood".
Anbar's Sunnis have fought each other before. In 2006, tribes banded together and helped U.S. troops dislodge Sunni al Qaeda militants who had gained control of most of the province.
The "Sahwa" (awakening) councils or the Sons of Iraq as they came to be known were later co-opted by the government and have come under increasing attack from Sunni militants who despise them as allies of the Shi'ite prime minister.
The al Qaeda-affiliated Islamic State of Iraq has been invigorated by the conflict in Syria, where mainly Sunni rebels, including Islamists linked to al Qaeda, are fighting to oust President Bashar al-Assad, who is backed by Shi'ite Iran.
Online videos show militants in target practice, emptying assault rifles in the vast desert of Anbar, which shares a porous border with Syria. Suicide bombings targeting Shi'ites, and attacks on security forces are spiking again.
The show of Sunni strength has spurred Shi'ites and Kurds to renew a bond forged by shared oppression under Saddam, a Sunni.
"We do not want that alliance to be spoiled by anything," said Kurdistan's foreign relations chief, Falah Mustafa Bakir.
A senior Kurdish delegation arrived in Baghdad on Monday to try to resolve differences between the central government and the autonomous Kurdistan region over land and oil rights.
"The Hawija incident and ensuing violence sounded the alarm among Kurds," said a senior Shi'ite leader on condition of anonymity.
"The conflicts and problems with a Sunni region would be more dangerous and complicated than the current issues and disagreement with the central government".