Clashes rage in rebel bastions of Syria’s Aleppo Brahimi, who previously served as envoy to Iraq and Afghanistan, replaces former U.N. Secretary-General Kofi Annan, who announced he would leave the post by the end of this month after failing to bring about a cease-fire despite months of negotiations. The announcement came just as U.N. observers in Syria were beginning to pack their things on Friday in preparation to close down their mission. Deployment of the observers was one of the only steps taken under Annan’s peace plan. The team was intended to watch over a cease-fire that never took hold, and so was left trying to chronicle some of the more egregious instances of bloodshed. Both sides have “chosen the path of war,” said the U.N.’s assistant secretary-general for peacekeeping, Edmond Mulet. The U.N. plans to keep a small liaison office to support any future peace efforts. The 17-month-old conflict between President Bashar Assad’s regime and rebels trying to bring him down has left some 20,000 people dead, according to estimates by anti-Assad activists. The escalating fight has in the past two months turned to battles in the country’s two main cities, Damascus and Aleppo — once firm bastions of Assad’s rule. Rebels have managed to keep fighting in both cities despite facing overwhelming regime firepower. In Damascus, activists reported heavy shelling and clashes in many areas Friday, including western districts believed to have rebel pockets. Damascus-based activist Moaz al-Shami described the shelling as “nonstop” and said gunners were firing from the Qassioun mountains overlooking the city. Regime forces have been fighting for nearly a month to crush the rebels’ footholds in Aleppo, in the north of the country. Rebels have been driven from some areas, but the report of clashes near the airport suggests the battles could be shifting to new fronts. Syrian refugee: Let Assad suffer, not die