ALEPPO, Syria - Syrian rebels fighting to oust President Bashar 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.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."He said the establishment of secure areas on the borders with Jordan and Turkey "was an essential thing that would confirm to the regime that its power is diminishing bit by bit."A no-fly zone imposed by NATO and Arab allies helped Libyan rebels overthrow Muammar Gaddafi last year. The West has shown little appetite for repeating any Libya-style action in Syria, and Russia and China strongly oppose any such intervention.Insurgents have expanded territory they hold near the Turkish border in the last few weeks since the Syrian army gathered its forces for an offensive to regain control of Aleppo, Syria's biggest city and economic hub.'Fateful, but not fatal setbacks'Rebels who seized swathes of the city three weeks ago have been fighting to hold their ground against troops backed by warplanes, helicopter gunships, tanks and artillery.One rebel commander named Yasir Osman, 35, told Reuters tanks had advanced into Salaheddine, despite attempts to fend them off by 150 fighters he said were short of ammunition."Yesterday we encircled the Salaheddine petrol station, which the army has been using as a base, and we killed its commander and took a lot of ammunition and weapons. This ammunition is what we are using to fight today," he said.Aleppo and the capital Damascus, where troops snuffed out a rebel offensive last month, are vital to Assad's struggle for the survival of a ruling system his family and members of his minority Alawite clan have dominated for four decades.Assad has suffered some painful, but not yet fatal, setbacks away from the battlefield, losing four of his closest aides in a bomb explosion on July 18 and suffering the embarrassment of seeing his prime minister defect and flee to Jordan last week.Syrian state television showed Assad swearing in Wael al-Halki on Saturday to replace Riyad Hijab, who had only spent two months in the job. Halki is a Sunni Muslim from the southern province of Deraa where the uprising began 17 months ago.The deputy police commander in the central province of Homs was the latest to join a steady trickle of desertions, said an official in the opposition Higher Revolution Council group."Brigadier General Ibrahim al-Jabawi has crossed into Jordan," the official told Reuters from Amman.At least 20 people were killed on Sunday in the second day of an armored offensive to retake the northern Damascus suburb of al-Tel from rebels, opposition activists said.Heavy artillery barrages were hitting the Sunni Muslim town as loyalist troops made a renewed push after an attempt to storm Tel on Saturday was repelled, several activists and Free Syrian Army sources in the area said.The Arab League said it had postponed a meeting of Arab foreign ministers scheduled for Sunday to discuss the Syria crisis and to select a replacement for Kofi Annan, the United Nations-Arab League envoy, and would set a new date.Deputy Arab League chief Ahmed Ben Helli told Reuters the meeting was delayed because of a minor operation undergone by Saudi Arabian Foreign Minister Prince Saud al-Faisal.Saudi Arabia, Qatar and Turkey are the leading regional supporters of the Syrian opposition. Assad's main backers are Iran and Lebanon's Shi'ite Hezbollah movement.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 realized that the absence of a no-fly zone to counter Assad's air superiority hindered rebel movements.He was speaking a day after US 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.