U.N. Special Envoy Staffan de Mistura voiced deep concern at the truce unraveling in Aleppo and at least three other hotspots

U.N. Special Envoy Staffan de Mistura voiced deep concern at the truce unraveling in Aleppo and at least three other hotspots, although he saw some narrowing of positions between the government and opposition visions of political transition.

"Hence my appeal for a U.S.-Russian urgent initiative at the highest level, because the legacy of both President Obama and President Putin is linked to the success of what has been a unique initiative which started very well. It needs to end very well," de Mistura told a news conference.

The United States and Russia must convene a ministerial meeting of major and regional powers who compose the International Syria Support Group (ISSG), he said.

"There is no reason that both of them which have been putting so much political capital in that success story and have a common interest in not seeing Syria ending up in another cycle of war should not be able to revitalize what they have created and which is still alive but barely."

The main opposition High Negotiations Committee (HNC) pulled out of the formal talks a week ago, in protest of intensified fighting and slow aid deliveries.