Rebel official says it is "completely out of the question" for them to withdraw from the divided city in northern Syria.
Syrian opposition fighters have rejected Russian demands that they withdraw from the northern city of Aleppo by Friday evening, according to an official in one rebel faction.
"This is completely out of the question. We will not give up the city of Aleppo to the Russians and we won’t surrender," Zakaria Malahifji, of the Fastaqim rebel group, told Reuters news agency on Wednesday.
Earlier on Wednesday, Russia had told rebels in Aleppo to leave by Friday evening, signalling it would extend a moratorium on air strikes against targets inside the city.
The Russian defence ministry said opposition fighters would be allowed to exit Aleppo unharmed and with their weapons between 9am and 7pm via two special corridors.
President Vladimir Putin had ordered the pause in fighting "to avoid senseless victims", the ministry said, saying that Syrian authorities would ensure that Syrian troops pulled back from the two corridors designated for rebels.
However, Malahifji said there were no safe exit corridors, as Russia had stated.
"It’s not true. Civilians and fighters are not leaving. Civilians are afraid of the regime, they don’t trust it. And the fighters are not surrendering," he said.
Aleppo has been hit by some of the worst violence in Syria’s long-running conflict, turning the once-bustling economic hub into a divided and bombed-out symbol of the war.
At the moment, Aleppo’s frontline runs through the heart of the city, dividing rebels in the east from government forces in the west.
Humanitarian pauses in the past have been largely unsuccessful, both in getting aid into eastern Aleppo and getting residents out of the city.
Fighters launched a major assault on Friday, backed by car bombs and salvos of rockets, to break through government lines and reach the 250,000 people besieged in Aleppo’s east.
Since then, opposition factions have amassed on Aleppo’s western outskirts in a bid to end Bashar al-Assad government’s three-month encirclement of the city’s eastern districts.
"Russia halted its air strikes on Aleppo in mid-October to allow a humanitarian pause for civilians and rebels to leave the city in safety," Al Jazeera’s Mohammed Adow, reporting from Gaziantep, on the Turkish side of the Syria-Turkey border, said.
"But Syrian government jets and helicopers have their raids on the city dropping barrel bombs, cluster bombs and bunker busters."
The latest attacks have been on neighbourhoods in western Aleppo recently taken by the rebels, our correspondent said.
"May God punish them for the air strikes that keep targeting us around the clock," Abu Ahmad, a western Aleppo resident, told Al Jazeera.
"The artillery and tank shells do not stop day and night, but we have no plans to escape."