Islamist rebels smashed the entrance of a 15th-century Timbuktu mosque on Monday, while their Al-Qaeda allies in northern Mali cut off the key city of Gao by planting landmines all around it. In Timbuktu, the Al-Qaeda-allied Islamist group Ansar Dine (Defenders of Faith) continued their destruction of the city\'s cultural treasures, defying a chorus of international condemnation. Some residents sobbed as the Islamists broke down what they call the \'sacred door\' of one of Timbuktu\'s three ancient mosques, Sidi Yahya -- closed for centuries due to local beliefs that to open it will bring misfortune. In Gao meanwhile, two sources said Al-Qaeda in the Islamic Maghreb (AQIM) and its allies had planted mines around the city, with one Tuareg rebel spokesman accusing them of taking the city hostage. Mossa Ag Attaher, spokesman for a Tuareg rebel National Movement for the Liberation of Azawad (MNLA), which until recently shared control of Gao with the Islamists, said the Islamists had \"mined the area surrounding Gao\".  AQIM, he said, was \"using the population as hostages, as a human shield to protect itself from an MNLA counter-attack\", he added. The North African Al-Qaeda franchise and their offshoot Movement for Oneness and Jihad in West Africa (MUJAO) forced their former MNLA allies out of the city in deadly clashes last week. \"Many people are trying to escape, to take the bus to go to Bamako, but the Islamists are stopping them,\" said Attaher, the MNLA\'s Paris-based spokesman. A west African source also confirmed that landmines had been planted around Gao \"to prevent a possible attack by troops\" from the west African regional bloc ECOWAS as well as a possible counter-offensive from the Tuareg fighters. In Timbuktu, the jihadists of Ansar Dine, who occupied Mali\'s vast north three months ago destroyed seven tombs of ancient Muslim saints over the weekend which they consider idolatrous. A spokesman said they were acting in the name of God and would \"destroy every mausoleum in the city. All of them, without exception\". Exclusive video footage obtained by AFP shows turbaned men chanting \'Allahu Akbar\' (God is great) while smashing a mausoleum with pick-axes in a cloud of dust, the mud-brick tomb showing gaping holes in the side with rubble piling up alongside it. They continued their work Monday at the 15th century Sidi Yahya mosque. A former tour guide in the once-popular tourist destination said: \"They came with pick-axes, they cried \'Allah\' and broke the door. It is very serious. Some of the people watching began crying.\" Another man, a relative of a local imam (religious leader), said he had spoken to members of Ansar Dine and \"they wanted to show that it is not the end of the world\" when the door is opened. According to the website of the UN cultural agency (UNESCO) Sidi Yahya is one of Timbuktu\'s three great mosques and was built around 1400, dating back to the city\'s golden age as a desert crossroads and centre for learning. The Organisation of Islamic Cooperation condemned the destruction, saying in a statement the sites were \"part of the rich Islamic heritage of Mali and should not be allowed to be destroyed by ... bigoted extremist elements.\" The fabled city, which became a metaphor for a mythic, faraway place, is considered one of the centres from which Islam spread through Africa in the 15th and 16th centuries. Ansar Dine began their campaign of destruction after UNESCO put Timbuktu on its list of endangered world heritage sites. Pleas have poured in for the Islamists to halt the destruction, reminiscent of the Taliban blowing up the giant Buddhas of the Bamiyan valley in Afghanistan -- an ancient Buddhist shrine on the Silk Road -- in 2001 after branding them un-Islamic. International Criminal Court prosecutor Fatou Bensouda on Sunday told AFP that those destroying the religious building could face prosecution. \"This is a war crime which my office has authority to fully investigate.\" United Nations chief Ban Ki-moon deplored the destruction of tombs, with his spokesman Martin Nesirky quoting him as saying: \"Such attacks against cultural heritage sites are totally unjustified.\" In a matter of months Mali has gone from one of west Africa\'s stable democracies to a nation gripped by deadly chaos.  A March 22 coup eased the way for Tuareg separatist rebels -- descendants of those who founded Timbuktu in the fifth century -- to seize an area larger than France, which they consider their homeland. However the previously unknown Ansar Dine group, fighting on their flanks seized the upper hand. Openly allied with Al-Qaeda in the Islamic Maghreb, they have since pushed the Tuareg rebels from all positions of power. The international community fears the vast desert area will become a new haven for terrorist activity and the Islamists have threatened any country that joins a possible military intervention force in Mali.