Early this year Sunni Arab worshippers in the Iraqi city of Fallujah were surprised to see an armed man in sunglasses instead of the regular sheikh ascend the mosque pulpit.
The visibly agitated moderate cleric stood aside, silenced by an Islamist militant preaching violence against Iraq's security forces.
"The man was wearing a dishdasha (Arab robe) and on top of that, a shoulder holster containing a gun," said one worshipper who asked not to be identified.
"The sheikh appeared extremely agitated. When the man delivered the sermon the sheikh kept staring at the floor like he didn't want to hear it."
The stifling of conciliatory voices among Iraq's Sunni Arab religious leaders bodes ill for prospects of quelling a Sunni Islamist insurgency that has taken hold of swathes of the country.
The armed man preached that it was halal, or permitted by religious law, to rob or kill members of Iraq's security forces, in a sermon meant as a slap in the face to the regular sheikh's edict a week earlier forbidding such acts.
Other sources in Fallujah, a city crowded with minarets and known as the "city of mosques", corroborated the worshipper's account, and said that militants now dictate the contents of Friday sermons.
Sunni militants have controlled the cities of Fallujah and parts of Ramadi in Iraq's mainly Sunni western Anbar province since early January, and last month Islamic State (IS) insurgents sharing their ideology overran vast tracts of Iraq's north.
- Wanted men -
The lightning onslaught began in the northern city of Mosul, where tribal and military sources say IS executed 13 Sunni clerics for failing to pledge allegiance to the group led by Iraqi jihadist Abu Bakr al-Baghdadi.
One of those killed was an imam at Mosul's Great Nur al-Din Mosque, where Baghdadi made a brazen public appearance on July 4 to deliver a Ramadan sermon.
In an unverified video posted online, Baghdadi calls from the mosque pulpit on Muslims to "obey" him, in a clear bid by the jihadist fighter and battlefield strategist for religious authority.
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Such tactics have sown fear among mainstream Sunni clerics.
"When Daash came to Fallujah, the imams and religious speakers did not receive a direct threat, but they left the city after they decided that there would be no religious common ground with emirs of Daash," said a Sunni cleric who declined to be named, referring to the Arabic acronym for IS.
The cleric is the brother of the worshipper who heard the inflammatory sermon in Fallujah. The worshipper called his brother after the sermon to warn him about what had happened.
"It has become a well-known sermon in Fallujah… Members of the security forces who do not repent to Daash, their funds are halal. Those who do not repent and give up their arms are wanted men," said the cleric, who has fled to the city of Kirkuk in Iraq's north.
"If I and other sheikhs go back to Fallujah now, you don't know what will greet you. Assassination? Treachery? You just don't know. Am I a wanted man?"
- Staying silent -
IS insurgents have not reached Baghdad, where Sunni cleric Ahmed al-Ani still feels confident enough to preach against the group.
"The path these people are treading is a blind one, which will lead to the abyss... These (people) do not represent Sunnis at all," he said.
"Everybody is exposed to danger... The fear is that everyone is silent, and puts their head in the sand."
But the message of moderate clerics is already being lost in the din of battle, as some among Iraq's minority Sunnis are enticed by Baghdadi's call to take up arms against a Shiite-led government many see as sectarian and oppressive.
IS propaganda online is slick and pervasive, drawing young and enthusiastic fighters from across the Middle East and even Europe and the United States.
The cleric in Kirkuk said he had been approached by a father desperate for him to talk to his son, who had grown his hair and beard and run off to join IS.
"I couldn't speak to him," the cleric said.
"I'm afraid he might slander me and say this man forbids me from jihad."