The United Nations envoy for Syria called on the United States and Russia to revive the war-torn nation’s stalled peace talks he said have been overshadowed by a recent flare in violence. Staffan de Mistura told reporters early Thursday the two-month-old ceasefire between Western- and Saudi-backed opposition and President Bashar Assad’s government “hangs by a thread.” De Mistura called on both the U.S. and Russia to intervene, adding that the legacies of both President Barack Obama and President Vladimir Putin were linked to the success of the talks. He said fighting would need to subside in order for the peace talks to move forward, but that it won’t happen “without some sort of political solution on the horizon.” At least 27 civilians were reportedly killed on Wednesday during government strikes on a hospital and nearby residential area in eastern Aleppo.