BEIRUT (AP) - Syrian forces unleashed a barrage of mortars and artillery on the battered city of Homs for hours before dawn on Saturday, sending terrified residents fleeing into basements and killing more than 200 people in what appeared to be the bloodiest episode in the nearly 11-month-old uprising, activists said. The government denied the assault. It said the reports are part of a "hysterical campaign" of incitement by armed groups against Syria, meant to be exploited at the U.N. Security Council as it prepares to vote on a draft resolution backing an Arab call for President Bashar Assad to give up power. With Syria growing increasingly chaotic, Western and Arab countries have stepped up their push for a U.N. resolution to pressure Assad. A vote was scheduled for Saturday, but negotiations were continuing to the last minute as Russia, a strong ally of Syria, signaled it would veto any call for Assad's removal. In a blunt warning to Washington, Foreign Minister Sergey Lavrov said Saturday that if a resolution is put to a vote without taking Russia's opinion into account it will only lead to "another scandal" at the Security Council. French Foreign Minister Alain Juppe countered that after the Homs bloodshed - which he called a "crime against humanity" - "those who block the adoption of such a resolution are taking a grave historical responsibility." Tunisia decided to expel Syria's ambassador in response to the "bloody massacre" in Homs and "no longer recognizes" the Assad regime, said an official in the president's office, speaking on condition of anonymity in line with government policy. Angry Syrians stormed their embassies in Berlin, London, Athens, Cairo and Kuwait city, clashing with guards and police and - in Cairo - setting fire to part of the embassy. Hours after the Homs assault eased, security forces in the Damascus suburb of Daraya opened fire Saturday on a funeral procession for victims of a shooting a day earlier, killing seven people, activists said. There were signs that the bombardment in Homs, Syria's third largest city, was in response to moves by army defectors to solidify their control in several neighborhoods. There were reports that defectors set up new checkpoints in several areas, and two activists from Homs said defectors attacked a military checkpoint in the Khaldiyeh district Thursday night and captured 17 soldiers. The activists spoke on condition of anonymity to protect themselves from retaliation. If defector activity was the spark, the assault signals a new willingness by the regime to unleash more devastating force against the dissidents. The defectors, part of a force called the Free Syrian Army, have grown increasingly bold in attacks on the military and attempts to take overt control in pro-opposition areas. Khaldiyeh, a mainly Sunni neighborhood in the mixed city, took the brunt of the assault. Residents described a hellish night of ceaseless shelling that sent them fleeing to lower floors and basements of buildings. "We were sitting at home and the mortars just started slamming into buildings around us," said Mohammad, a Khaldiyeh resident. "There was nothing that prompted it, not even protests ... people are terrified today," he added by telephone. Mohammad, who like other Syrians in Homs declined to be further identified, said the shelling started shortly before midnight and lasted until the early morning hours Saturday. He said residents were out Saturday inspecting the damage, looking for relatives. It's a catastrophe, no other way to describe it. Online video by activists showed chaotic scenes in a makeshift clinic set up in what appeared to be a Khaldiyeh mosque, the room filled with wounded men with gashes and broken limbs being bandaged. Several dead bodies were shown. In another video, fire ravaged a house that had been shelled, as people desperately poured water on the blaze. The videos could not be independently verified. Residents said most shelling came from a military installation west of Khaldiyeh and Alawite-dominated neighborhoods to the east. Syria's Alawite minority, who belong to an offshoot of Shiite Islam, forms the backbone of Assad's regime and the military leadership. The government denied the assault and said corpses shown in amateur videos were of people kidnapped by "terrorist armed groups" who filmed them to portray them as victims of the alleged shelling. Homs is a hotbed of dissent to Assad's regime and is known to shelter a large number of army defectors. Ammar, a resident of the Bab Tadmur district of Homs, said the real death toll exceeded 330, and hundreds of others were wounded. We are being massacred, what is the Security Council still waiting for? The Syrian National Council, Syria's main opposition group, put the toll at more than 220. It called on Russia to stop its "shameful intransigeance" at the U.N. and for the world to take action to stop the bloodshed. Assad is trying to crush the revolt with a sweeping crackdown since March. But neither the government nor the protesters are backing down. The opposition, which began with peaceful protests, has turned more and more to arms, and clashes with the military have thrown many parts of the country into relentless violence. This month, the regime has seemed to have stepped up its use of force to stamp out the defectors. Last week, the military launched a heavy assault in the suburbs east of Damascus after dissidents showed greater control there. Three days of fighting ensued in residential areas, killing several hundred, until the regime appeared to have silence the dissidents for now. The U.N. said in December that that more than 5,400 people have been killed since March, but it has been unable to update its count for weeks due to the chaos. The U.N. Security Council is scheduled Saturday to take up the Syria resolution, and diplomatic efforts continued to the last minute to try to avert a Russian veto. U.S. Secretary of State Hillary Rodham Clinton was to meet Saturday with Russia's Lavrov on the sidelines of a security conference in Berlin. Lavrov said the latest version of the resolution resolves "quite a number of things which were important to us." But, he said, it makes too few demands of anti-Assad armed groups, and Moscow remains concerned about whether it prejudges the outcome of a national dialogue among political forces in Syria that it is trying, with little success, to arrange. The U.S. and its partners have ruled out military action but want the global body to endorse an Arab League plan that calls on Assad to hand power over to his vice president. AP writers Elizabeth A. Kennedy in Beirut, Anita Snow at the United Nations, Aya Batrawy in Cairo and Bouazza ben Bouazza in Tunis contributed to this report.