Whole streets of Aleppo are in flames after cluster bombs thought to have been dropped by Syrian government forces or their Russian allies targeted rebel-held areas of the city.

The attacks came hours after some of the heaviest bombing for months in the devastated city, following the breakdown of a ceasefire and vows by President al-Assad's forces to launch a major new offensive.

At least 12 people are known to have died in the latest bombardment, in Bustan al-Qasr district, which comes after at least 49 people were killed in the city on Wednesday (21 September). The death toll is thought to be higher but doctors say

they have not had time to update the numbers killed and injured because hospitals - often targeted by bombing raids - are under intense pressure. One doctor told The Guardian: "The pressure on the hospitals is very dire."

The renewed assault on Aleppo comes as aid convoys struggle to reach the city, much of which has been destroyed as a result of the five-year civil war. The Syrian army announced a major new offensive on the city was underway, according to reports by Reuters).

Up to two million civilians remain trapped in the city. Ibrahim Alhaj, a spokesman for Aleppo's Civil Defence search-and-rescue, said: "for anyone who hears the airstrikes from yesterday, at 7 p.m., until now, they would say it is a world war in Aleppo," he said according to the Telegraph.

In an interview with western media President al-Assad says the United States deliberately targeted his troops in air strikes on 17 September, killing at least 60 troops and possibly many more. He also denied targeting hospitals, which have been regularly destroyed in Aleppo and other cities, and defended the use of barrel bombs.

"A bomb is a bomb, what's the difference between different kinds of bombs?" al-Assad told Associated Press. "All bombs are to kill, but it's about how to use it. When you use an armament, you use it to defend the civilians. You kill terrorists in order to defend civilians."

The US has blamed the Syrian regime and its ally Russia for the attack on an aid convoy on Monday in Urem al-Kubra in which more than 20 civilians were killed. Russia denies involvement and claims the convoy did not appear to have been attacked from the air. US Secretary of State launched an angry attack on the claims at the United Nations, saying: "The trucks and the food and the medicine just spontaneously combusted. Anybody here believe that?" (CNN).