Russia-backed Syrian government forces also have won significant gains this week in the rebel-held eastern part of Aleppo.
Moscow intervened militarily in support of Damascus previous year but says it is not involved in the current assault on Aleppo.
Syrian state media says a town northeast of the capital Damascus has been cleared of rebel fighters after an agreement with the government, and an opposition monitor estimates that almost 2,000 gunmen and their family members have left.
"Unsanitary conditions and overcrowding are already challenges in a congested city with few open spaces", he said, pointing out that even before the latest exodus from east Aleppo there were already some 400,000 displaced people in the government-held west of the city.
The UN, the Syrian Red Crescent and Russian Federation have been administering aid to those who have made it to west Aleppo.
The front lines around the rebel-held sector of Aleppo have mostly held steady since Monday, when insurgents were forced from more than a third of the area they have controlled for several years in an assault by the Syrian army and its allies. The National Coalition leader, Anas al-Abdeh, used language similar to O'Brien's, writing that government forces transformed parts of Aleppo "into a coffin".
The talks have been going for about two weeks and are the first between Russian Federation and rebel groups who say they have been abandoned by the West.
Meanwhile, Turkey and Russian Federation, two of the biggest backers of opposing sides in the war, agreed on the need for a halt to fighting on Thursday in order to deliver aid.
Syrian Kurdish fighters have dislodged armed opponents of President Bashar al-Assad's regime from a northern district.
Cavusoglu said the failure to find a political solution in Syria will breed more extremists.
Germany's Foreign Minister Frank-Walter Steinmeier also called for "temporary truces" in Syria to allow for a humanitarian corridor.
The humanitarian situation continues to deteriorate in Syria's Aleppo City, where an estimated 31,500 people are displaced from areas in eastern Aleppo retaken by the government of Syria, China's Xinhua news agency reported quoting United Nations (UN) spokesman Stephane Dujarric.
In preparation for street-by-street fighting in these districts, hundreds of fighters from Syria's elite Republican Guard and Fourth Division arrived in Aleppo on Friday, according to the Observatory.
More than 300 civilians, including dozens of children, have been killed in east Aleppo since the offensive began, according to the Observatory. "But, at this stage, we have to be realistic that the person who kills nearly 600,000 people should not rule any country", he said during a visit to Lebanon.
Meanwhile, a monitoring group said on Friday that Syrian troops had taken control of half of the militant-held areas in eastern Aleppo.
"They are moving in on the ground, but they are afraid of ambushes because of the density of residents and fighters", he said.