Syrian opposition groups who broke the siege of opposition groups-held eastern Aleppo on Saturday in a significant territorial gain came under intense air attack from pro-government forces on Sunday trying to repel the advance which also cut government-held Aleppo's main supply route. Opposition groups have taken most of a large government military complex southwest of Aleppo city in a major offensive begun on Friday to break a month-long siege and are now attacking further into government held territory. The surprise advance in Ramousah allowed fighters from insurgent areas in western Syria to break through a strip of government-controlled territory on Saturday and connect with fighters in the encircled sector of eastern Aleppo. But fierce fighting and continuous Russian and Syrian air strikes in and around the Ramousah area mean no safe passage for besieged east Aleppo residents has been established, activists and the Syrian Observatory for Human Rights said. Fighters from a coalition of opposition groups called "Jaish al Fateh" announced the start of a new phase to liberate the whole of Aleppo, saying it pledged to increase the numbers of fighters for the battle it said will only end by hoisting their flag on the ancient Aleppo citadel in government hands. Jets believed to be Russian intensified their bombing of opposition-held Aleppo countryside and also hit opposition held Idlib city in north western Syria, opposition groups said. They released video footage that showed huge flames of fire it said was caused by white phosphorus bombs dropped on the city.

Syria's Bashar Assad wants to take full control of Aleppo, pre-war Syria's most populous city, which has been divided between opposition and government-held areas. Assad's government forces are supported in Syria by Russian air power, Iranian militias and fighters from Lebanon's Hezbollah group who have sent reinforcements to shore up the army. Opposition groups' gains this weekend could change the balance of power in Aleppo, after Assad said a siege by government and allied forces on opposition-held east Aleppo in early July was a prelude to re-taking the city. The loss of Aleppo would be a crushing blow for opposition groups. "We have now seized full control of the Ramousah area...We are in our trenches but there are insane air strikes of unprecedented ferociousness. The regime is using cluster and vacuum bombs," said Abu al Hasanien, a senior commander in Fateh Halab, the coalition of moderate opposition groups inside the city. Pro-Syrian government news channels have mostly played down the opposition groups' gains and say Syrian army efforts have caused opposition groups to withdraw from some recently-gained areas.

The opposition front line is now pushing northwest into western held Aleppo on the edges of the Hamdaniya neighborhood and a housing estate called the 3,000 project, opposition groups and the Observatory said. North of Hamdaniya in the direction of the opposition groups' push is another large government military complex, the Assad military engineering academy. The opposition Syrian National Coalition (SNC) congratulated opposition groups on making "spectacular gains (which send) a clear message to the Assad regime, Iran and Russia that they will not be able to defeat the Syrian people or dictate the terms of a settlement."

Fears are growing in government-held western Aleppo that it might become besieged by opposition groups, as east Aleppo has been by government forces, because the main route south to Damascus for goods transport, the Ramousah road, has been severed. News of the opposition groups' advance caused food prices to rise by as much as four times in western Aleppo, the Observatory said. Following the cutting of the main Ramousah road, Observatory director Rami Abdurrahman told Reuters military vehicles can still get in out of west Aleppo through remaining exit roads to the north, but these are not safe enough for civilians. In eastern Aleppo, despite some scenes of celebration as fighters broke the siege yesterday, the lack of a safe route out means conditions for residents remain unchanged. Three vans of vegetables crossed into east Aleppo, Abdurrahman said, but this was a symbolic gesture and the corridor is too dangerous for civilians or significant supplies to pass. The United Nations and humanitarian agencies have said conditions in isolated opposition-held east Aleppo have become very concerning. "Most recently I'm hearing that the markets are closed and it's next to impossible to purchase food. The U.N. estimates that collectively all aid supplies in east Aleppo will only last about two more weeks," Christy Delafield, senior communications officer for Mercy Corps, which runs the largest non-governmental aid operation inside Syria, told Reuters.

Residents of both sides of the city have been living in fear of competing sieges of their neighborhoods in recent weeks. The rebel advance at the weekend cut off a key regime access route on the city's southern edges, which had been used to bring in supplies for the estimated 1.2 million residents of western districts. Overnight, regime forces brought in dozens of trucks carrying food and fuel into the western neighborhoods via the northern Castello Road, according to the Observatory. "This is the new route that the regime forces are securing as a temporary alternative to the route they previously depended on," Abdel Rahman said. Syrian state television Al-Ikhbariyah confirmed that "fuel, food, and vegetables entered Aleppo city." A military source in Damascus denied that the city's west had been besieged, saying "the situation is under control and the situation is not worrisome." Seven trucks of fruits and vegetables entered the eastern rebel-held districts on Sunday and were quickly purchased by residents.