It is becoming known as the war of the fatwas: the dizzying exchange of proclamations between Islamic moderates and militants on what it means to be Muslim. The duels have been waged everywhere from pamphlets to cyberspace.
Now some Muslim leaders seek to shift tactics against radicals. Their hope rests in one of Islam's most elemental questions: Who has the real authority to make religious rulings and other interpretations of the faith?
Proposals to sharply control the issuing of fatwas - the nonbinding edicts on Muslim life, law and duties - are still little more than loose concepts and would require potentially stormy challenges to Islam's traditions of decentralised leadership.
But there are some influential backers such as Jordan's King Abdullah II. They argue that bold changes are needed in Islam's hierarchy to isolate radical clerics and discredit terrorist leaders, including Osama bin Laden, who have used self-styled religious decrees to justify their views and actions.
Abdullah, who brought his anti-terrorist message to Athens last week, has appealed for moderate Muslims to take decisive control over fatwas and religious guidance. In early December, Abdullah told the 56-member Organisation of the Islamic Conference (OIC) that failure to establish a clear framework to interpret Islam leaves the door open for radicals to strengthen their ranks.
The summit in Mecca, Saudi Arabia - Islam's holiest site - wrapped up with a statement reinforcing that only "those who are authorised" can issue fatwas. The monarchs, prime ministers and other delegates, however, could reach little common ground on a proposal to give a single body of Islamic law experts greater oversight of all fatwas covering the Muslim world.
It was a sample of the huge religious and political complications that stalk any efforts to change the centuries-old fatwa practices.
Islamic scholars say it would require a fundamental shift away from Islam's traditions that spread religious authority far and wide rather than under a single leader or institution. Some powerful centres of Islamic learning, such as Egypt's Al-Azhar University, also resist reforms that could diminish their theological voice.
"Religious authority is in the eyes of the beholder and not anywhere else," said Abdullahi An-Na'im, an expert in Islamic law at Emory University in Atlanta. "This reality has not changed in 15 centuries of history, and will not change now."
But now there is the Internet and other ways to spread messages to mass audiences - which some commentators have dubbed "the war of the fatwas."
One of the most infamous salvos was the February 1998 "fatwa" by bin Laden and followers that called on Muslims to "kill the Americans and their allies." It has been blamed for inspiring some of the most staggering terrorist strikes, including the September 11 attacks.
Other militants increasingly have followed suit with fatwa-style declarations of their own - including statements attributed to terrorist chief Abu Musab al-Zarqawi, the alleged mastermind of the November 9 hotel bombings in Amman, Jordan, which killed 60 people.
Moderates clerics initially were slow to react to the radical fatwas. But now there is a potent counterattack.
In March, Spain's Muslim leaders issued a fatwa condemning al-Qaida on the anniversary of the 2004 train bombings in Madrid that claimed 191 lives. A similar anti-terrorist fatwa was made by Britain's largest Sunni Muslim group following the July attacks that killed 52 commuters.
Jordan announced in December it will prosecute clerics who promote violence or issue fatwas without state permission, becoming the latest Muslim nation seeking to muzzle radical Islam.
"The fatwa, unfortunately, has become a tool of terrorists," said Abdulssalam Al-Abbadi, Jordan's former religious affairs minister. "We cannot keep having two versions of Islam: the correct and moderate views and the violent and extremists views. It's tearing apart the faith."
Many Westerners first learned of fatwas through the 1989 decree by the founder of Iran's Islamic Revolution, the late Ayatollah Ruhollah Khomeini, to kill British author Salman Rushdie for perceived insults to Islam in his book "The Satanic Verses." But mainstream fatwas are not intended as mandates and rarely have anything to do with violence.
They are essentially opinions from Islamic scholars covering everything from proper conduct during religious pilgrimages to family relationships and dating. One popular Web site - "Ask Imam Online" - even gets down to questions such as whether it is permissible for women to pluck their eyebrows. The reply was yes.
Fatwas, however, are not binding and views on the same subject can vary. They gain force from consensus among experts in Islamic law and traditions. Yet attempts to establish a single authority for fatwas would likely meet with extreme resistance, some Islamic theologians predict.
"It's impossible," said Ashirbek Muminov, a researcher on Islam at the Kazakh Oriental Studies Institute in Almaty, Kazakhstan.
It goes beyond fighting ancient traditions, he added. Many Muslims - particularly in former Soviet republics - will distrust "official" imams and others given oversight powers, he said.
"In each place Islam has lots of local peculiarities and to gather all that in one place is very difficult," said Muminov.
But not all experts see insurmountable problems.
They note that only a fraction of Muslims believe militants such as bin Laden can make legitimate religious edicts without the benefit of systematic theological training. The established view is that fatwas can come only from those grounded in Islamic jurisprudence, known as "fiqh."
The struggle for moderate Muslims is to raise somehow the "serious issue ... that the so-called fatwas of radical Islamists shouldn't be taken as authoritative," said James Turner Johnson, a Rutgers University religion professor.
"But I don't see the radicals giving up the practice of issuing their own fatwas," he added. "Doing so wraps their message in a familiar religious form and gives it at least a superficial authority. It tends to establish them as the 'real' leadership of Muslims."