DAMASCUS — Warplanes mounted the heaviest air strikes in months against rebel-held districts of the city of Aleppo overnight, rebel officials and the Syrian Observatory for Human Rights said on Thursday.

There was no immediate comment from the Syrian military on the reports, or mention of Aleppo air strikes on state media.

U.S. Secretary of State John Kerry demanded on Wednesday that Russia and the Syrian government immediately halt flights over Syrian battle zones, in what he called a last chance to salvage a collapsing ceasefire and find a way “out of the carnage”.

Zakaria Malahifji, head of the Aleppo-based Fastaqim rebel faction’s political office, said it was the most intense bombardment since April. “There is no weapon they didn’t use,” he told Reuters from Turkey.

President Bashar al-Assad said in an interview with AP News broadcast on Thursday that Syria’s war will “drag on” as long as it is part of a global conflict funded and interfered in by other
countries.

“When you talk about it as part of a global conflict and a regional conflict, when you have many external factors that you don’t control, it’s going to drag on,” Assad said.

The conflict has wrought a devastating human toll, killing hundreds of thousands, displacing half the country’s pre-war population of 22 million and included poison gas attacks, starvation sieges and raids on hospitals.

Assad told AP that Russia was not behind a deadly attack on an aid convoy on Monday, for which U.S. officials have said they believe Moscow was responsible.

“Those convoys were in the area of the militants, the area under the control of the terrorists. That’s what they should accuse first: the people or the militants, the terrorists
who are responsible for the security of this convoy,” Assad said.

“We don’t have any idea about what happened.”

The United States and Russia have been leading diplomatic efforts to negotiate a lasting ceasefire and have been discussing how to coordinate attacks on militants from the Islamic State and the group formally known as the Nusra Front.

Assad cast doubt on the intentions of the United States in Syria, saying it “doesn’t have the will” to fight militants.

“I don’t believe the United States will be ready to join Russia in fighting terrorists in Syria…the United States is not genuine regarding having a cessation of violence in Syria,” he said.

Assad said U.S. strikes, which killed 62 Syrian government troops in Deir ez-Zor on Sept. 17, were “intentional” and they lasted for an hour. He added that the US “does not have the will” to join Russia in fighting terrorists in Syria.