Syrian rebels fighting to oust President Bashar al-Assad need the protection of no-fly zones and safe havens patrolled by foreign forces near the borders with Jordan and Turkey, a Syrian opposition leader said.Battles raged on Sunday in the northern city of Aleppo, where tanks, artillery and snipers attacked rebels in the Saif al-Dawla district next to the devastated area of Salaheddine.Syrian civilians desperate to check on their homes pushed into fluid front lines around Salaheddine, even as sniper fire cracked out and rebels warned them to stay away.Abdelbasset Sida, head of the Syrian National Council, said the United States had realised that the absence of a no-fly zone to counter Assad's air superiority hindered rebel movements.He was speaking a day after U.S. Secretary of State Hillary Clinton said her country and Turkey would study a range of possible measures to help Assad's foes, including a no-fly zone, although she indicated no decisions were necessarily imminent."It is one thing to talk about all kinds of potential actions, but you cannot make reasoned decisions without doing intense analysis and operational planning," she said after meeting Turkish Foreign Minister Ahmet Davutoglu in Istanbul.Though any intervention appears to be a distant prospect, her remarks were nevertheless the closest Washington has come to suggesting direct military action in Syria."There are areas that are being liberated," Sida told Reuters by telephone from Istanbul. "But the problem is the aircraft, in addition to the artillery bombardment, causing killing, destruction."