Fighters have accepted similar government amnesty offers in other besieged areas in recent months, notably in Daraya, a suburb of Damascus.
Fighters have accepted similar government amnesty offers in other besieged areas in recent months, notably in Daraya, a suburb of Damascus that was under siege for years until rebels surrendered it in August.
However, rebels said they had no plan to evacuate Aleppo, the last major urban area they control, and denounced the amnesty offer as a deception.
"It's impossible for the rebel groups to leave Aleppo because this would be a trick by the regime," Zakaria Malahifji, a Turkey-based official for the Fastaqim group which is present in Aleppo, told Reuters. "Aleppo is not like other areas, it's not possible for them to surrender."
Washington was also skeptical of government motives: "For them to suggest that somehow they're now looking out for the interests of civilians is outrageous," White House spokesman Josh Earnest said, citing the heavy civilian toll from air strikes and bombardment.
The army announced a reduction in shelling and air strikes on Wednesday to allow people to leave. It backed that up with an ultimatum: "All those who do not take advantage of the provided opportunity to lay down their arms or to leave will face their inevitable fate."
The government also sent text messages to the mobile phones of some of those people trapped in the besieged sector, telling them to repudiate fighters in their midst. More than 250,000 people are believed to be trapped inside rebel-held eastern Aleppo, facing dire shortages of food and medicine.
Speaking to Danish television, Assad said he would "continue the fight with the rebels until they leave Aleppo. They have to. There's no other option."
He said that he wanted rebels to accept a deal to leave the city along with their families and travel to other rebel-held areas, as in Daraya. Neither Assad nor his generals gave a timeline for rebels to accept their offer.
Washington accuses Moscow and Damascus of war crimes for intentionally targeting civilians, aid deliveries and hospitals to break the will of those trapped in the besieged city. Russia and Syria accuse the United States of supporting terrorists by backing rebel groups.
A U.S. official, speaking on condition of anonymity, said that the relentless Russian and Syrian bombardments could result in the fall of rebel-held eastern Aleppo within "weeks if not days".
"It’s unclear how long they will last, but considering the destruction of infrastructure that supports life, they are hanging by a thread," the U.S. official said. "There is only so much they can endure.
The war has already killed hundreds of thousands, made half of Syrians homeless, dragged in global and regional powers and left swathes of the country in the hands of jihadists from Islamic State who have carried out attacks around the globe.
The United States and Russia are both fighting against Islamic State but are on opposite sides in the wider civil war, with Moscow fighting to protect Assad and Washington supporting rebels against him.
Storming Aleppo's rebel-held zone, which includes big parts of the densely populated Old City, could take months and cause a bloodbath, the U.N. Syria envoy warned on Thursday.
"The bottom line is in a maximum of two months, two and a half months, the city of eastern Aleppo at this rate may be totally destroyed," said Staffan de Mistura, invoking the 1990s atrocities of the Rwandan genocide and Yugoslavia's civil war.