After meeting Syrian opposition negotiator Riad Hijab, Ayrault strongly condemned the Assad government's bombing of the besieged city "where nearly 300,000 people live, lacking food, medicine and medical care".
"There is a strategy of total war, which can only result in the partition of Syria and strengthening Daesh [the Islamic State armed group]," he told the AFP news agency.
Russian forces are not taking part in the current assaults on Aleppo, but are bombing the neighbouring province of Idlib.
Syrians trapped between regime and terrorists
Speaking at a World Policy Conference in Doha earlier, Ayrault declared that the Syrian people are "caught in a vice" between a "barbarous regime" and "terrorist groups lacking any scruples at all".
"Some people claim that we just have to choose the lesser of two evils: leave the task of getting rid of Daesh to the regime of Bashar al-Assad," he said in a reference to Mosow's justification for its backing of Assad.
He called for "more to be done to maintain an alternative to the bloody regime of Bashar al-Assad" and argued that the provinces of Iraq that have been seized from IS should become "examples of peaceful coexistence and governance that respects diversity".
Assad government rejects Aleppo autonomous administration
Syria will not accept a Un proposal of an autonomous rebel adminstration in east Aleppo, Assad's Foreign Affairs Minister Walid Muallem said after meeting UN peace envoy Staffan de Mistura in Damascus on Sunday.
"We told him that we reject that completely," he told reporters. "How is it possible that the UN wants to reward terrorists?"
On Sunday rebels retaliated with a barrage of rockets into the government-held west of the city, killing at least eight children at a school in the Furqan neighbourhood, according to Syrian state media.