As flames leaped high in the battered northern Syrian city of Aleppo, hopes faded anew Thursday for any revival of Syria's broken cease-fire.
In a week meant to showcase the diplomatic drive to shore up the truce, rush humanitarian aid to the country's hardest-hit areas, isolate and target jihadist fighters and lay the groundwork for moves toward a political solution to the grinding five-year conflict, efforts faltered on all fronts.
A day after Secretary of State John F. Kerry appealed for the grounding of aircraft over key aid routes, the heaviest airstrikes in months pounded opposition-held districts of Aleppo, killing dozens of people, witnesses and activists reported Thursday.
Video from the city and outlying areas showed massive fires apparently fueled by incendiary weapons.
President Bashar Assad, in a rare interview published Thursday, blamed the United States for the breakdown of the Sept. 12 truce and accused Washington of lacking the will to confront the militants of Islamic State _ claims the State Department branded "ridiculous."
Assad, in the wide-ranging interview with The Associated Press, rejected American accusations that the U.N. convoy was hit by Syrian or Russian planes. He also denied that Syrian forces were preventing aid deliveries to opposition-held parts of Aleppo, or using barrel bombs against civilians _ both well-documented practices.
Syria's multisided war has been marked by the indiscriminate targeting of civilian areas, but Assad was dismissive when questioned about his methods.
"When you have terrorists, you don't throw at them balloons, or you don't use rubber sticks for example," he said. "You have to use armaments."
Moscow, for its part, declared that Kerry's no-fly proposal was infeasible. The state-run Tass news agency quoted Russian Deputy Foreign Minister Sergei Ryabkov as saying that the U.S. plan "won't work." He blamed those seeking to oust Assad by force for driving the conflict and the attendant humanitarian crisis.
In one bright spot amid a grim landscape, U.N. trucks bearing badly needed supplies made their way to the rebel-held Damascus suburb of Muadhamiya, the U.N. said. Deliveries had been on a 48-hour hiatus after a large aid convoy outside Aleppo was attacked Monday night, killing about 20 civilians.
But the world body said security fears were preventing vital deliveries to other besieged areas, which are home to an estimated 1 million Syrians. Jan Egeland, the U.N. special adviser on humanitarian affairs, said at a briefing in Geneva that 40 aid trucks were poised at the Turkish-Syrian frontier, unable to proceed to areas including Aleppo's rebel-held east.
Describing Monday's convoy strike as the worst incident of its kind in the course of the conflict, Egeland called for an independent inquiry into the attack, asking how humanitarian workers could be expected to continue their "sacred service to the Syrian people" under threat of more attacks.
"Let this be the turning point," he told reporters. "Let this be the bleakest moment."
In New York, more talks were being held Thursday on the sidelines of the U.N. General Assembly by the International Syria Support Group, made up of envoys from world powers trying to resolve the conflict.
Beforehand, Syrian opposition groups released a letter saying they would not support a resumption of the truce unless consequences for violating it were spelled out _ warning that without such enforcement mechanisms, violence would rage unchecked.
