Bamako, Mali (CNN) -- Elderly men were keeping watch Saturday over Timbuktu's main library after Islamists burned a tomb listed as a UNESCO World Heritage site.
The attacks Friday were blamed on Ansar Dine, a militant group that seeks to impose strict Sharia law.
The ancient city in Mali was captured by at least two separatist Tuareg rebel groups -- one of which is Ansar Dine -- in an anti-government uprising in the northern part of the country that began in January.
The rebels burned the tomb of a Sufi saint where people come to pray, said Sankoum Sissoko, a tour guide familiar with the place. He said the library and other heritage sites remained under threat.
Baba Haidara, a member of the National Assembly, called for UNESCO and the greater international community's help restoring the shrine and freeing the city.
"They attacked the grave, broke the doors and windows and ripped and burned pieces of white clothing that surrounded the tomb of the saint in front of everyone," said Haidara, who is from the central Mali city. "With their attack, the militants touched the heart of Timbuktu. They picked Friday because they know many people visit the shrines on this day."
Sufism is a mystical dimension of Islam, and Islamists believe Sufi shrines are sacrilegious. As such, they have mounted attacks against Sufi sites in several nations.
Sissoko said the attackers were dressed in signature Ansar Dine black robes and turbans. Timbuktu residents, he said, were ready to take up arms against the rebels, who have been linked to al Qaeda.
Religious leader Baba Cheick Sekou said the occupying rebel groups have no respect for Timbuktu's religious and historic importance.
Sekou said he feared for the protection of the prestigious Koranic Sankore University and ancient manuscripts that are kept there, as well as other tombs and mosques of historic significance.
"All Muslims know the tomb is a holy place," he said. "It's not something you attack and destroy. It's anti-Islamic. People in the community are angry."
Haidara described the shrine situation as bad.
"The young people of Timbuktu have started training to resist the militants, and I fear people will seek revenge," he said.
Timbuktu Mayor Ousmane Halle said the attackers tore down windows and wooden gates at the grave sites and burned them. Tensions were high in the city, he said.
"People are angry, and for a good reason," Halle said.
"So far there's been no response from the central government condemning the attack," he said. "I'm still waiting for them to give a declaration. That's what they would have done if it happened in (Mali's capital city of) Bamako."
To many, Timbuktu conjures a distant and exotic place due its location on the southern edge of the vast Sahara and accounts of great material and scholarly wealth.
Known as the "city of 333 saints" for the Sufi imams, sheiks and scholars buried there, Timbuktu was declared a UNESCO World Heritage site in 1988. UNESCO is a United Nations cultural organization.
After the ouster of Moammar Gadhafi, armed Tuaregs who had been fighting in Libya streamed back across the border into Mali. In March, the ongoing Tuareg revolt sparked a military coup against Mali President Amadou Toumani Toure by officers unhappy with the government's handling of the rebellion.
The rebels capitalized on the chaos in Bamako, in southern Mali, and usurped large swaths of territory in the north. UNESCO grew gravely concerned about the protection of heritage sites.
UNESCO chief Irina Bokova has called for all groups to respect and protect the city's history.
"Timbuktu's outstanding earthen architectural wonders that are the great mosques of Djingareyber, Sankore and Sidi Yahia must be safeguarded," she said.
"Along with the sites' 16 cemeteries and mausolea, they are essential to the preservation of the identity of the people of Mali and of our universal heritage."
Islamists destroyed another world heritage site in 2001 when the Taliban used dynamite to blow up two giant 6th century statues of Buddha carved into the cliffs of Bamiyan in central Afghanistan.
In a recent report, Human Rights Watch accused the Tuareg rebels of war crimes, including rape, use of child soldiers, summary executions and pillaging of hospitals, schools, aid agencies and government buildings.
Journalist Katarina Hoije contributed to this report.