BEIRUT —Renewed airstrikes killed at least 20 civilians as they fled government advances in Syria’s besieged eastern part of Aleppo Tuesday, opposition groups reported as troops continued to target the enclave controlled by rebel groups. The United Nations said up to 16,000 people have already been displaced in recent days of fighting.

A senior military official in Damascus put the number of people fleeing the opposition-controlled area Tuesday alone at around 20,000, saying his government has put security measures in place to vet those leaving to ensure no fighters are among them and no violence takes place.

The official, speaking to The Associated Press on condition of anonymity in line with regulations, denied any arbitrary detentions or revenge attacks took place during the influx of displaced, dismissing such reports as a distraction from his troops’ swift success in penetrating rebel defenses.

The U.N. estimates that 275,000 residents are trapped in the area that has been under tight siege and heavy bombardment since July. Many residents and rights groups have expressed fear of revenge or retaliation attacks during the dramatic government advances that have cleaved the territory held by opposition fighters since 2012.

France called for an urgent Security Council meeting to discuss the situation in Aleppo, where ferocious fighting continued as government forces closed in and sought to break down rebel defenses in the deeply divided city, once Syria’s thriving commercial center.

Government forces pushed their way into a new neighborhood on the edge of the rebel-held areas to the east, near the Aleppo airport road, according to the opposition Syrian Observatory for Human Rights. The Britain-based Observatory and government allied media reported pro-government troops were also battling opposition fighters on the western edge of government-controlled Aleppo, seeking to secure the areas and repel opposition fighters from them.

The Russian Ministry of Defense said Tuesday that “half” of eastern Aleppo has been “liberated.”

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