"The [regime] attacks are very intense. More than 40 people have been injured," Najib al-Ansari, a civil defense official in Aleppo, told Anadolu Agency.
"The injured were taken to exit points specified by the ceasefire/evacuation deal, but all these points were closed," al-Ansari said, adding that none of the injured were allowed out of besieged areas.
On Tuesday evening, the Assad regime and Syrian opposition forces agreed to a Turkey-brokered ceasefire to allow for the evacuation of civilians from eastern Aleppo.
Abdul-Mumin Zeineddin, for his part, a coordinator for the armed opposition in Aleppo, told Anadolu Agency that regime forces and allied militias were still trying to push into opposition-held parts of the city.
"Iran rejected the deal and hasn’t allowed the city to be evacuated. It has also laid down some conditions of its own," Zeineddin said.
"We will fight on until victory or death," he added.
According to eyewitnesses in Aleppo who spoke to Anadolu Agency, Syrian regime forces and allied militias on Wednesday committed several fresh ceasefire breaches.
Pro-regime forces used mortar and artillery fire to attack Aleppo’s opposition-held Al-Sukkari, Al-Ansari, Al-Mashhad, Saladin and Saif al-Dawla districts, witnesses said.
Regime forces, they added, had also stopped injured people from being evacuated from besieged areas in violation of the ceasefire deal.
Recent days have seen Assad regime forces reestablish control over parts of Aleppo captured four years ago by armed opposition groups.
Syria has been locked in a devastating civil war since early 2011, when the Assad regime cracked down on pro-democracy protests -- which had erupted as part of the "Arab Spring" uprisings -- with unexpected ferocity.
Since then, hundreds of thousands of people are believed to have been killed by the conflict and millions more displaced.