Rebels opened a corridor to the east for the month of August after pro-government forces first applied a blockade in July, but they were not able to hold it as the government and its Russian ally pounded the gap with artillery and airstrikes.
"In just a few days, we will open the way for our besieged brothers", rebel commander Abu Mustafa told AFP from the frontline district of Dahiyet al-Assad, on the southwestern outskirts of Aleppo. The attack began with a massive explosion that struck government positions on the front line, said Yasser al-Yousef of the Nour el-Din el-Zinki group, one of the main factions in east Aleppo.
While they scored an initial advance, the offensive has since slowed, according to the Syrian Observatory for Human Rights, a Britain-based monitor.
Syrian insurgents on Sunday kept up their shelling of government-controlled areas of Aleppo, killing at least seven people, including three children, state TV reported, and pushing their way with auto bombs and tanks into new territory in the western part of the city.
Once Syria's economic powerhouse, Aleppo has been ravaged by the conflict that began in March 2011 with anti-government protests and has since killed more than 300,000 people.
Despite this apparent extension of the halt in Russian raids, "many people think it's only a matter of time before Russia and its allies launch the final assault on Aleppo", Challands said.
Chris Doyle, from the Council for Arab-British Understanding, a London-based advocacy group, said the failure to end the siege of Aleppo has unified the disparate rebel groups, with hard-line fighters taking the lead.
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East Aleppo has been subjected to a ferocious campaign of aerial attacks by Russian and Syrian government warplanes, and hundreds of people have been killed in recent weeks, according to opposition activists and trapped residents.
Also yesterday, the 15-member body issued a second statement, condemning the widely reported attacks on a school complex in Haas village, Idlib governorate, on 26October, which killed at least 22 children and teachers, and on a school in the western part of Aleppo on 28 October, which killed a number of children, and called for impartial investigations.
But Kremlin spokesman Dmitry Peskov said Putin "considers it inappropriate at the current moment", adding that the president thought it necessary to "continue the humanitarian pause" in Aleppo.
Despite Russian air support, the Syrian regime has had limited success in its attempts to seize the whole of Aleppo.
According to Syrian state news agency SANA, three civilians were killed in rebel fire on Aleppo on Monday.
"The only thing that has been accomplished is partial control over Dahiyet al-Assad", a neighbourhood on Aleppo's western outskirts that rebels entered on Friday, he said.
"Those who argue that this is meant to relieve the siege of eastern Aleppo should be reminded that nothing justifies the use of disproportionate and indiscriminate weapons, including heavy ones, on civilian areas and it could amount to war crimes", De Mistura said.