Syria Rebels Seize Border Posts as Residents Flee Damascus BEIRUT, Lebanon - Rebel fighters in Syria, building on the momentum gained by their brazen assassination of three top security officials a day earlier, seized all four border crossings with Iraq and one into Turkey on Thursday, while also claiming for the first time to have captured a pocket of Damascus after intense street fighting. SANA, via Agence France-Presse - Getty Images. President Bashar al-Assad swearing in Gen. Fahad Jassim al-Freij as the new defense minister in Damascus, in this handout photo from Syrian state TV. The government fought back hard, with no indication that its far superior military machine had lost its edge against an opposition still working predominately with small-caliber weapons. Helicopters blasted the northern Damascus suburb of Qaboun with rockets, while the armed forces warned residents of a wide area of the southern part of the capital to evacuate ahead of an assault. Thousands of people fled to neighboring Lebanon. "They threatened them and gave them 24 hours to leave their homes or they will be shelled," said Ali Salem, an activist reached via Skype. Even residents in the western Damascus neighborhoods of Mezze and Kafr Souseh, who were not warned, fled in droves as shells thudded into their neighborhood from military positions on the Qassioun mountain above Damascus. But the government tried to project an aura of calm, even as it unleashed its forces in a manner similar to the devastating assaults on restive cities like Homs, where neighborhoods were effectively flattened and all the residents driven out. President Bashar al-Assad appeared for the first time since the bombing attack Wednesday that killed three senior security officials. The Syrian leader showed up on state television to swear in the new defense minister to replace the one assassinated in a bomb attack. The ceremony for Gen. Fahd Jassem al-Freij - the broadcast showed the two men interacting without any sound - seemed to take place in Damascus in one of the presidential palace's reception rooms, its wall décor a series of distinctive antique doors inlaid with mother-of-pearl that used to grace homes in old Damascus. Wire service reports said that Mr. Assad had fled to Latakia, the coastal city where he has a home, just one of the many rumors swirling around the capital in the wake of the stunning assassinations. One opposition activist said that only the women and children of the Assad family had flown to the coast - not unusual for a hot July weekend. More intense fighting loomed, as the United Nations Security Council deadlocked as expected over a resolution seeking to punish Syria with economic sanctions for not putting a cease-fire into effect. Russia and China vetoed a resolution focused on the Syria crisis for a third time in an acrimonious meeting. A last-ditch compromise was expected to give a 30-day extension for the 300 observers who suspended their work on June 16 because of the heavy violence. The departing officer in charge of the United Nations observers, Gen. Robert Mood, said at a news conference in Damascus that the monitors were "irrelevant" without the will for peace on both sides. Little such will was in evidence. If there was an image for the day, it came from the border crossing, where rebels raised their flag. One video posted online showed rebel fighters defacing pictures of Mr. Assad and his father and predecessor as president, Hafez al-Assad, as they overran one border crossing after another. At the Bab al-Hawa entrance from Turkey, a fighter wielding a large stick smashed a huge hole in the president's portrait over the border crossing. In Baghdad, Iraqi government officials confirmed the seizures of the four crossings and said the frontier was shut and additional Iraqi troops sent there as a precaution. One top Iraqi government official, who spoke on condition of anonymity because he was not authorized to discuss the matter, said the border crossings, in Anbar and Nineveh Provinces, were closed and that Iraqi border forces had witnessed the executions of several Syrian Army soldiers at the hands of the Free Syrian Army rebels. Neil MacFarquhar reported from Beirut, and Tim Arango from Baghdad. Reporting was contributed by Dalal Mawad and Hwaida Saad from Beirut, Yasir Ghazi from Baghdad, Alan Cowell from London, Rick Gladstone from New York, Eric Schmitt from Washington, and an employee of The New York Times from Anbar Province, Iraq.