Two sides in conflict over whether there should be limits to the liberty of self-expression clashed violently in a usually tranquil side street on the Right Bank of Paris.

When it was over, a dozen people lay dead — including some of the most prominent political cartoonists and satirists in France, and the police officers assigned to protect them.

Wednesday's attack at the offices of the newspaper Charlie Hebdo seems the latest chapter in a clash of values between the West and a version of militant Islam that is at least a quarter-century old, beginning when Ayatollah Khomeini, Iran's supreme leader, issued a 1989 fatwa calling for the assassination of novelist Salman Rushdie, accused by some conservative Muslims of blasphemy.

In France, the conflict over what limits to place on press freedom has often involved the satirical weekly, whose mix of crude, often obscene artwork and brashness has few if any parallels in Anglo-Saxon media.

Press freedom and the right to self-expression in general differs vastly in the world, with even a generally liberal country like Sweden passing laws that criminalize hate speech and prohibiting expressions of contempt directed against a group or one of its members.

Depending on the political system or climate, critiquing the ruler or the government may be a red line that few dare to cross — treated as taboo, criminal or even treasonous. In extreme cases, some governments have sought to extend their bans on criticism outside their own borders, attacking dissidents abroad, or using diplomatic means to quell insults or demand respect.

Few forms of criticism are as sensitive or divisive as those touching on religious belief or ideology, or inspire the lethal fury demonstrated in the attack on Charlie Hebdo.

In 2006, the left-leaning, iconoclastic tabloid, which regularly skewers a wide range of targets from the Vatican to Hollywood, reprinted 12 cartoons of the Prophet Muhammad whose original publication by a Danish newspaper touched off riots in some Muslim nations. Some Muslims were outraged that their religion's founder was being made fun of, or even depicted at all.

Five years later, after Charlie Hebdo published a spoof issue supposedly guest-edited by Muhammad, its offices were firebombed and its website hacked.

The publication has been sued by several French Muslim organizations, accused of publishing racist cartoons, but won acquittal. In 2012, French police detained a man suspected of threatening to decapitate the editor-in-chief.

This week, the publication's front page featured one of France's most controversial writers, Michel Houellebecq, whose latest book imagines France in a not-too-distant future after an Islamic government takes power.

Also in the latest edition, Charlie Hebdo editor Stephane Charbonnier contributed the caricature of what clearly is meant to be a Muslim extremist — a bearded man with a Kalashnikov and an Afghan-style hat — hinting at a terrorist attack sometime this month in France.

Charbonnier, whose pen name was "Charb," was one of those killed Wednesday.

In 2012, speaking to The Associated Press, he defended his magazine's right under France's laws safeguarding the freedom of expression to print crude, lewd caricatures of Islam's founder.

"Muhammad isn't sacred to me," he said. "I don't blame Muslims for not laughing at our drawings. I live under French law. I don't live under Quranic law."

At that time, though, the French government, as well as the White House, openly questioned not the magazine's right to print, but its good judgment. At least 30 people had already been killed in violent protests over an amateur U.S anti-Islam video that portrayed the religion's founder as a fraud, womanizer and child molester.

"Is it pertinent, intelligent in this context to pour oil on the fire?" French Foreign Minister Laurent Fabius asked then. "The answer is no."

In the wake of Wednesday's bloodbath, such calls for editorial restraint vanished. French President Francois Hollande, speaking outside Charlie Hebdo's office, said the gunmen had targeted journalists striving to "defend their ideas, and to defend precisely the freedom that the Republic protects."

"We are threatened because we are a country of liberty," Hollande said.

Paris Mayor Anne Hidalgo mourned the slain cartoonists and journalists as "martyrs of freedom, of freedom of the press, the pillar of democracy," and called upon all freedom-loving people to hold a solemn march in their memory Thursday.

President Barack Obama denounced an attack on the "values that we share with the French people — a universal belief in the freedom of expression."

But in some parts of the world, the mass slaying at Charle Hebdo were celebrated because it was deemed to have outrageously and repeatedly abused its freedom to mock and shock.

A member of the al-Qaida in Yemen extremist organization, posting on the Twitter social network, accused the weekly of engaging in the "defamation of Islam." As news of the killings in Paris reached the Middle East, celebratory gunfire was reported in a Palestinian refugee camp in southern Lebanon

Rushdie, who spent years in hiding for fear of Islamist death squads, said Wednesday the clash of values is a stark and irreconcilable one, between the art of satire as a "force for liberty" on the one hand, and "tyranny, dishonesty and stupidity" on the other.

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Associated Press writers Jon Gambrell and Sarah El Deeb contributed from Cairo.