'Battle is in Damascus' as Syrian tanks fire in 12-hour exchange Undeterred by international condemnation, the Syrian military continued its unrelenting shelling of the city of Homs. DAMASCUS, Syria -- Residents of Syria's capital spoke about a night of shooting and explosions in the worst violence during the uprising against President Bashar Assad. The nearly 12 hours of fighting in Damascus suggested a new boldness among armed rebels, who previously kept a low profile in the capital. It also showed a willingness by the regime to unleash in the capital the sort of elevated force against restive neighborhoods it has used to crush opponents elsewhere. For the first time in the uprising, witnesses said, regime tanks opened fire in the city's streets, with shells slamming into residential buildings. "Yesterday was a turning point in the conflict," said Maath al-Shami, an opposition activist in the capital. There were clashes in Damascus that lasted hours. The battle is in Damascus now. Blasts shook the neighborhoods of Qaboun and Barzeh until about 1:30 a.m. on Saturday. "We spent a night of fear," one resident said, speaking on condition of anonymity for fear of reprisals. The resident said the shooting and explosions in the capital "were the worst so far." As tanks fired shells, troops clashed with rebels in the two neighborhoods, al-Shami said via Skype. He said at least four people were killed. The battles began when troops opened fire on anti-Assad protest marches and rebels responded, witnesses said. In one brazen attack, the rebels struck a power plant in Qaboun with rocket-propelled grenades, setting fire to a generator and causing blackouts. The attack left buses charred and smashed a car. A video of the aftermath taken by U.N. observers said a soldier was killed in the RPG attack. One resident said a large sports venue, the Abbasid stadium, had been transformed into an army barracks as the military tried to reinforce the capital, and that increasing numbers of checkpoints had been set up. Earlier, a car bomb aimed at a bus carrying security men exploded in a Damascus suburb, killing at least two, the Syrian Observatory for Human Rights said. Troops also clashed with rebels from the Free Syrian Army in Damascus' Kfar Souseh district when rebels attacked a military checkpoint. The FSA, which groups defectors from the Syrian military with protesters who have taken up weapons, had made an unusually public appearance Thursday night in Kfar Souseh, overtly joining a large opposition rally. The bolder moves were a strong sign the ragtag group is pushing to take its fight to the regime's base of power. At least 17 killed in Daraa, activists say To the south, regime forces heavily shelled a district of the city of Daraa until the early hours Saturday, smashing homes, according to activists. Daraa is the city where the uprising against Assad's regime first erupted in March 2011. "People were taken by surprise while in their homes," Adel al-Omari, a local activist, said of the shelling, including mortar fire that hit the Mahata district. The Britain-based Syrian Observatory for Human Rights said 17 people were killed in the shelling. The Local Coordination Committees said 19 civilians lost their lives, include a father and two children from one family and five members of another family. The LCC and the Observatory also reported shelling and clashes in the central city of Homs, one of the main battlegrounds of the uprising. Both groups said troops stormed Homs' posh neighborhood of Ghouta and the Observatory said security forces are conducting raids and searching for wanted people in the area. U.N. releases massacre video Also Saturday, U.N. observers in the country ostensibly to monitor the cease-fire issued the first independent video images from the scene of a reported massacre last week in a remote farming village. Activists say up to 78 people, including women and children, were shot, hacked and burned to death in Mazraat al-Qubair on Wednesday. The video, taken in the U.N. visit a day earlier, showed blood splashed on a wall pockmarked with bullet holes and soaking a nearby mattress. A shell punched through one wall of a house. Another home was burnt on the inside with dried blood was splashed on floors. One man wearing a red-and-white checked scarf to cover his face, pointed at a 2008 calendar adorning a wall, bearing the photo of a lightly-bearded, handsome man. "This is the martyr," the resident, sobbing. He sat on the floor, amid strewn colorful blankets, heaving with tears. It was not immediately clear if he was a resident of the village or related to the man in the photograph. "They killed children," said another unidentified resident. My brother, his wife and their seven children, the oldest was in the sixth grade. They burnt down his house. After the observers' visit, U.N. spokeswoman Sausan Ghosheh said the scene held evidence of a "horrific crime" and that the team could smell the stench of burned corpses and saw body parts strewn around the now deserted village, once home to about 160 people. She said residents' accounts of the mass killing were "conflicting," and that the team was still cross checking the names of the missing and dead with those supplied by nearby villagers. Opposition activists and Syrian government officials blamed each other for the killings. Activists accused pro-government militiamen known as "shabiha." A government statement on the state-run news agency SANA said "an armed terrorist group" killed nine women and children before Hama authorities were called and killed the attackers. Report: Journalist says rebels tried to get him killed Thousands have been killed since the crisis began in March last year. The U.N.'s latest estimate is 9,000 dead, but that is from April and it has been unable to update it. Syrian activists put the toll at more than 13,000. The latest escalations are another blow to international envoy Kofi Annan's peace plan, which aims to end the country's bloodletting. Annan brokered a cease-fire that went into effect on April 12 but has since been violated nearly every day since and never properly took hold. Russia on Saturday indicated it would not oppose the departure of Assad if such a move is a result of a dialogue between Syrians themselves and is not enforced through external pressure. "If the Syrians agree between each other, we will only be happy to support such a solution," Foreign Minister Sergei Lavrov told reporters.