Hundreds of civilians fleeing war-torn Aleppo are being detained and questioned by the Syrian government, observers say.
A spokesperson for the Syrian military immediately denied the claims made by the UK-based Syrian Observatory for Human Rights (SOHR), insisting people fleeing rebel-held areas are being checked in case "terrorists" are among them.
The unnamed sourced added that any unknown people are taken to "specific places" in areas where other civilians are located.
An estimated 20,000 people have been forced to flee eastern Aleppo in four days following significant ground advances by Syrian government forces against rebels in a new offensive that has caused international alarm.
Many of them are reported to have fled to safer ground in areas under government or Kurdish control.
In a major breakthrough in the push to retake the whole city, regime forces captured six rebel-held eastern districts of the city over the weekend.
A senior official in the military alliance supporting President Bashar al Assad said the Syrian army and its allies aimed to capture all rebel-held eastern areas by the time President-elect Donald Trump takes office.
Aleppo is seen as a vital strategic prize for the Syrian government as it is the last city still holding out against President Assad's regime and it controls trade and military supply routes to Turkey.
Opposition forces have lost a third of their territory in Aleppo, according to the SOHR, which declared the government offensive the rebels' "worst defeat since they seized half the city in 2012".
The group said a government artillery attack on a housing area on Wednesday morning, where those displaced by the fighting had sought refuge, killed at least 21 people.
Syria's Red Crescent is offering assistance in government-held areas, but does not yet have access to eastern Aleppo.
"I can only imagine how difficult the situation must be for people who fled into the places where aid workers and supplies are not or scarcely available," said spokesperson Pawel Krzysiek.
"The situation of those fleeing is desperate."
Unverified video posted on Twitter by Syrian journalist Ahmad Alkhatib showed several bodies strewn across an unidentified, bloodied street in eastern Aleppo being put into body bags by Syrian volunteers the White Helmets, which put the death toll at 45.
The pictures included images of men, women and young children wrapped-up in coats and gloves with bags and suitcases as they apparently attempted to flee the fighting.
Meanwhile, the Lebanese Al Manar TV channel reported pro-government forces were advancing in the southern portion of the city's rebel enclave.
