The Syrian Observatory for Human Rights said air strikes and artillery fire hit the besieged, rebel-held eastern districts of Aleppo on October 23.
The London-based monitoring group said government forces advanced on the southern outskirts of Aleppo, seizing territory overlooking the rebel-held areas of Rashideen and Khan Tuman.
The fighting killed at least 20 fighters, mostly from the former Al-Qaeda affiliate, the Fateh al-Sham Front, the monitor said.
Rebel shelling also hit two western neighborhoods on October 23, the monitor said.
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.
"You have various parties to the conflict and those with influence and they all have to be on the same page on this and they are not," said David Swanson, a spokesman for the UN humanitarian office.
No aid has reached Aleppo since July 7, with UN chief Ban Ki-moon warning that food rations would run out by the end of the month.
French Foreign Minister Jean-Marc Ayrault, who visited a camp for Syrian refugees in Turkey on October 23, urged the international community to "do everything" to end the "massacre" in Aleppo and resume efforts to reach a political agreement.
"We cannot come to a negotiation under the bombs," he said.
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.
Damascus and Moscow accuse rebels of allying with extremist groups. It is thought that some rebel forces are coordinating efforts with groups that have been labeled as terrorist by the United States and Russia.