BAGHDAD (AP) -- A militant extremist group's unilateral declaration of an Islamic state is threatening to undermine its already-tenuous alliance with other Sunnis who helped it overrun much of northern and western Iraq.
One uneasy ally has vowed to resist if the militants try to impose their strict interpretation of Shariah law.
Fighters from the al-Qaida breakaway group Islamic State of Iraq and the Levant have spearheaded the offensive in recent weeks that has plunged Iraq into its deepest crisis since the last U.S. troops left in 2011. The group's lightning advance has brought under its control territory stretching from northern Syria as far as the outskirts of Baghdad in central Iraq.
In a bold move Sunday, the group announced the establishment of its own state, or caliphate, governed by Islamic law. It proclaimed its leader, Abu Bakr al-Baghdadi, a highly ambitious Iraqi militant with a $10 million U.S. bounty on his head, to be the caliph, and it demanded that Muslims around the world pledge allegiance to him.
Through brute force and meticulous planning, the Sunni extremist group -- which said it was changing its name to simply the Islamic State, dropping the reference to Iraq and the Levant -- has managed to effectively erase the Syria-Iraq border and lay the foundations of its proto-state. Along the way, it has battled Syrian rebels, Kurdish militias and the Syrian and Iraqi militaries.
Now, the group's declaration risks straining its loose alliances with other Sunnis who share the militants' hopes of bringing down Iraq's Shiite-led government but not necessarily its ambitions of carving out a transnational caliphate. Iraq's minority Sunnis complain they have been treated as second-class citizens and unfairly targeted by security forces.
Topping the list of uneasy allies is the Army of the Men of the Naqshabandi Order, a Sunni militant organization with ties to Saddam Hussein's now-outlawed Baath Party. The group depicts itself as a nationalist force that defends Iraq's Sunnis from Shiite rule.
A senior Naqshabandi commander in Diyala province northeast of Baghdad told The Associated Press that his group has "no intention" of joining the Islamic State or working under it. He said that "would be a difficult thing to do because our ideology is different from the Islamic State's extremist ideology."
"Till now, the Islamic State fighters are avoiding any friction with us in the areas we control in Diyala, but if they are to change their approach toward our fighters and people living in our areas, we expect rounds of fighting with the Islamic State's people," said the commander who goes by the nom de guerre of Abu Fatima.
A second Naqshabandi leader in Diyala, in the Sunni town of Qara Tappah, also dismissed the notion of submitting to the militants' vision.
"We reject the caliphate rule presented by them. We are totally different from the Islamic State," said the commander, who goes by the name of Abu Abid. He too said that so far relations have been friendly enough, but that residents are wary of what the future may hold.
"Their number is small but we are afraid of the future when their number in the town becomes big," he said. "We know that these militants are treacherous and they plan to eliminate any competition, but we are ready to stop them."
If history is any guide, they have reason to worry. In Syria, the Islamic State of Iraq and the Levant also cooperated with many rebel groups after initially pushing into the country in spring 2013. Over time, however, it moved against its erstwhile allies and eventually crushed them.
It has followed a similar pattern in imposing its strict interpretation of Islamic law, choosing to overlook some practices it considers forbidden before eventually tightening its grip and implementation.
In Iraq's second-largest city of Mosul, which the insurgents overran earlier in June, they issued rules but have not rigidly enforced them. Signs emerged Sunday that tactics may be changing there.
Residents said three or four armed men in Afghan-style clothing but speaking in Iraqi accents told cafe owners in the Ghabat -- a wooded area dotted with cafes and popular with locals -- to stop serving water pipes, or shisha, saying it is forbidden under Islamic law. Other cafes in the city followed suit out of fear, and traders in Mosul were told Monday to stop importing the water pipes to the city, residents said.
The showcase of the extremist group's vision of its Islamic state is Raqqa, a city of 500,000 in northern Syria along the Euphrates River. Since expelling rival rebel groups this spring from the city, the militants have banned music, forced Christians to pay an Islamic tax for protection, and killed violators of its interpretation of Islam in the main square, activists say.