By Tom Heneghan, Religion Editor
PARIS (Reuters) - The grim sacking of Sufi shrines in Timbuktu is the latest chapter in an assault on prized religious heritage across the Muslim world that has picked up over the past decade with the spread of radical Islamism.
The world got a first taste of this iconoclasm in 2001, when Afghanistan's ruling Taliban blew up two huge 6th-century statues of Buddha despite an international outcry.
Since then, radical Islamists have also struck holy sites of other faiths, especially Christian churches. But their most frequent targets have been mosques and shrines of other Muslims loyal to a version of Islam less puritanical than their own.
This violence has spread through Pakistan, starting near the Afghan border and fanning out to strike famous Sufi shrines as far away as Lahore and southern Punjab.
It broke out in the Middle East last year when, in the wake of the Arab Spring, once-repressed Salafi groups destroyed shrines in Egypt. In Libya, some militants dug up Sufi saints' graves and dumped their remains on garbage heaps.
Like the radicals' strict theology, this assault on rival religious heritage goes back to the dawn of Islam and is rigorously enforced in its birthplace, Saudi Arabia.
Sanda Ould Boumama of the Ansar Dine group now reducing Timbuktu's tombs to rubble told France's RFI radio: "When the Prophet (Mohammad) entered Mecca, he said all the mausoleums should be destroyed. And that's what we're repeating."
Arch-conservative Sunnis - notably Saudi Wahhabis, other Salafis they inspired and Afghan and Pakistani Taliban - reject idolatry as un-Islamic and aim to destroy any trace of it.
Many targets are Sufis, a mystical school of popular Islam, because they revere saints and sages with ornate shrines and joyous festivals that they say help bring them closer to God.
The radicals also target Shi'ites and Ahmedis, a sect that believes another prophet came after Mohammad, as well as non-Muslims, noted Jamal Elias, Religious Studies Department chair at the University of Pennsylvania.
"At the root, there is a dividing line among Sunni Muslims between those who believe in intercessionary models of religion, and those who don't," he said.
Believers in intercession say the living can pray to a dead saint to ask God to help them. Strict Sunnis insist there can be no mediator between man and God.
The spread of Salafism through the Muslim world in recent decades means these conflicts are almost bound to break out when certain conditions prevail, said Mark Sedgwick, professor of Arab and Islamic studies at Denmark's Aarhus University.
"They believe they have a duty to enforce good and prevent evil," he said, so these attacks are "something that can happen when there is a breakdown of law and order."
Destroying rival sites is also part of the pattern of establishing the new religious order, Elias said.
"When they bring an area under their version of Islamic rule, they make certain kinds of gestures to show the place has now become virtuous," he said.
"They restrict the movement of women. They smash video rental and music shops. And they attack 'bad' Muslim practice."
In this logic, local protests against the destruction of holy places and objects only serve to convince the radicals that their argument is right. "They take that reaction as evidence that the people have fetishised the objects," Elias said.
In the famed city of Timbuktu, known as the City of 333 Saints, Al-Qaeda-linked Salafis took pick-axes and shovels to mausoleums of local saints and tore down a mosque door that locals believed had to stay shut until the end of the world.
They also smashed traditional African statues.
In Pakistan, where the majority of Muslims belong to the Sufi-inspired Barelvi sect, the local Taliban regularly stage bombings and bloody assaults on Sufi and Shi'ite sites.
The size or splendor of the shrines hardly deters them. In 2010, extremists bombed the Lahore mausoleum of Data Ganj Baksh, one of Pakistan's most famous Sufi sites, killing 42 people.
A year later, during the annual festival at another large shrine in southern Punjab far from the Afghan border, two more bombers killed 41 worshippers and injured scores more.
Several small Sufi shrines near Cairo were destroyed soon after Hosni Mubarak's fall from power last year. In Qalyoub, only quick action by residents saved their shrine from Salafi youths hacking away at it with crowbars and sledgehammers.
The fall of Muammar Gaddafi in neighboring Libya left many Sufi shrines defenseless. In January of this year, extremists bulldozed their way into a Benghazi cemetery and carted off the remains of 29 respected sages and scholars to dump elsewhere.
When militants threatened Libya's biggest shrine at Zlitan in March, armed volunteers rushed there in pick-up trucks mounted with anti-aircraft weapons to defend it.
Saudi Arabia has set an example by systematically destroying many historic Islamic sites in the name of its puritan Wahhabi version of the faith, lest they attract idolatrous worshippers.
The first wave came in the early 1880s, when tribesmen from central Arabia first conquered the holy cities of Mecca and Medina. They flattened the Medina cemetery where Mohammad's family was buried and almost tore down the Prophet's tomb.
The Ottomans drove them out and rebuilt many tombs, but the Saudis destroyed them again when they retook the cities in 1925. Historic Islamic sites have disappeared apace since then as the oil-rich kingdom has remade the holy cities.
"The Saudis have been on a long project to essentially build a new Mecca," said Elias, naming several mosques and tombs now replaced by modern buildings and parking lots.
"Look at the huge clock tower they've built," he said, referring to 600-metre (1,970 feet) tower that stands amid several high-rise hotels overshadowing the Grand Mosque. "It's part of this plan to erase the pre-modern era."
(Reporting By Tom Heneghan; Editing by Giles Elgood)