Intense fighting in the central Syrian city of Homs has left 60 to 70 percent of a besieged rebel-held district damaged, destroyed or uninhabitable, activists said on Sunday. The estimate from the Syrian Observatory for Human Rights came nine days into an all-out army assault on the rebel-held Khaldiyeh and Old City neighbourhoods, which have been under siege for more than a year. On Sunday, regime forces subjected insurgent areas of the city to fierce shelling, said the Observatory. \"Sixty to 70 percent of buildings in Khaldiyeh are either totally destroyed, partially destroyed, or unsuitable for habitation,\" Observatory director Rami Abdel Rahman told AFP. Homs is Syria\'s third-largest city, and tens of thousands of its residents have fled the fighting. \"Of all Syria\'s cities, Homs has suffered the highest levels of destruction... Images of Homs make it look like a world war has hit the city. Much of it has been flattened,\" he added. Amateur video posted online by activists on Sunday showed flames and thick black smoke rising from several empty burnt-out buildings already riddled with holes. Some structures shown in the video are barely standing. \"Even if the regime takes the neighbourhoods back, there\'s barely a house left standing to return to,\" said Abdel Rahman. \"It would even be dangerous to return. People from Homs are constantly under regime surveillance wherever they are in Syria, because their city has served as a rebel bastion since early in the revolt\" against President Bashar al-Assad. On Sunday, government troops used mortars, rocket fire and heavy artillery to target rebel areas in the city, the Britain-based Observatory said. On the edges of Khaldiyeh, fresh clashes broke out between rebels and troops and pro-regime militiamen, it added. According to the United Nations, some 2,500 to 4,000 people are trapped in the besieged areas. In Damascus, regime warplanes targeted Jubar in the east of the capital, while tanks hit Qaboon in the northeast, said the Observatory. Several mortar rounds hit Yarmuk Palestinian refugee camp in southern Damascus, it added, as rebels and troops clashed nearby. In northern Damascus, the army tried to storm Barzeh, where rebels are still holed up, the watchdog said. Syria\'s 27-month war has killed more than 100,000 people, the Observatory estimates. On Saturday alone, at least 69 people were killed nationwide, it said.