Fighting is continuing in the besieged, rebel-held neighborhoods of eastern Aleppo, a day after the end of a 72-hour "humanitarian" cease-fire that had been declared by Syria's government and its main ally, Russia.
The Syrian Observatory for Human Rights said air strikes from either Syrian or Russian warplanes began again on October 22 after a three-day lull.
The monitoring group, which relies on a network of on-the-ground sources, said there were also ground clashes and heavy artillery shelling along the front lines in the city.
Aleppo is divided between government-held districts and those controlled by opposition forces.
Some rebel forces are also thought to be coordinating efforts with groups that have been labeled as terrorist by the United States and Russia.
But Russian and Syrian government air strikes focusing on the heavily populated rebel-held eastern part of Aleppo have caused international outrage.
That has led to condemnation from the United States and the European Union leaders and calls from some EU member states for fresh international sanctions against the Syrian government and its supporters -- Russia and Iran.
Russia announced a "humanitarian pause" on October 20, and the Syrian Army opened eight corridors for evacuations, but just a handful of people crossed through a single passage.
The United Nations estimates more than 250,000 civilians are still trapped in the besieged rebel-held neighborhoods of the city.
The UN had hoped to use the cease-fire to evacuate seriously wounded people, and possibly deliver aid.
But it said it was unable to do so in the absence of security and safety guarantees for aid workers.
Meanwhile, a fresh UN inquiry has found Syrian government forces responsible for a third toxic-gas attack in Syria.
A report of the attack was submitted by the UN and the Organization for the Prohibition of Chemical Weapons to the UN Security Council on October 21.
It says Syrian government forces were responsible for helicopter strikes using barrel bombs filled with toxic gas, probably chlorine, in Qmenas in the Idlib Governorate on March 16, 2015.
In August, UN investigators blamed Syrian government forces for two earlier chemical attacks in Syria that involved the use of chlorine gas.
With reporting by AFP, Reuters, AP