The United Nations Security Council was due to hold an emergency session on Syria in New York on Tuesday, as the government of Syrian President Bashar al-Assad faces its biggest challenge from Sunni opposition fighters in the past eight years. 

The UN’s special envoy for Syria, Geir Pedersen, warned on Sunday that the dramatic escalation that saw al-Qaeda offshoot Hayat Tahrir al-Sham drive regime forces out of Aleppo in a lightning offensive that it launched on Nov. 27 posed severe risks to civilians. Pedersen called on the warring parties to protect civilians and resolve their differences through “meaningful and substantive negotiations” in keeping with a 2015 UN resolution aimed at ending the war. 

The violence showed no signs of abating as Syrian regime and Russian forces mounted a counterattack, intensifying airstrikes on Monday on the HTS stronghold of Idlib and positions around Aleppo that are aimed at keeping HTS and its Turkish-backed Sunni allies from advancing further south toward Hama. 

The White Helmets rescue organization said the strikes had targeted residential areas of Aleppo city and a displaced people’s camp in Idlib province where seven people were killed. Five of them were children.