The U.N. Special Envoy for Syria says eastern Aleppo could be “totally destroyed” by the end of the year due to the “cruel, constant” military activities in city where some 275,000 civilians are besieged.

At a news conference Thursday, U.N. envoy Staffan de Mistura and his Special Advisor, Jan Egeland, also called on the rebel group al Nusra to see the destruction and devastation their actions are causing on the civilians of the country.

“1,000 of you are deciding on the destiny of 275,000 civilians,” de Mistura said. He also criticized the Russians for what he said was excessive bombing of eastern Aleppo, putting the civilians of the city at risk for a comparatively small number of rebel fighters.

WATCH: De Mistura on situation in Aleppo

IS claims Syria border bomb blast

Also Thursday, the Islamic State group claimed responsibility for a bomb blast that killed at least 20 people, most of whom were Turkish-backed opposition fighters along Syria’s northwestern border with Turkey.

A suicide car bomber targeted a convoy of rebel troops near the border crossing in the village of Atmeh, just a short distance away from where the rebels and the jihadist group had been fighting along another stretch of the border.

The Syrian Observatory for Human Rights, a British-based non-profit group, put the number of dead at 21.

The Islamic State group took credit for the attack in an online statement.

Those killed include a judge and another top civil judicial figure from the rebel-held eastern Aleppo, according to a rebel official.

One witness told Reuters most of those killed in the blast were members of the Failiq al-Sham group, which has been fighting alongside Turkish soldiers to defeat the IS group.

 
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