Dozens of people are reported to have been killed in fierce clashes between rebel groups and government forces in the divided Syrian city of Aleppo.

The Syrian Observatory for Human Rights said rebels advanced into government-held western districts overnight but were pushed back by yesterday morning.

The battle was the most intense in Aleppo for more than a year, it added.

Russia later said attacks by

humanitarian disaster. Large parts of the city have been destroyed and its infrastructure has been severely damaged, leaving civilians without water and electricity.

The UN Security Council will discuss the violence in Aleppo later yesterday.

Meanwhile, US and Russia have agreed to work with Syria's warring parties to extend a shaky truce to the city of Aleppo, the State Department said yesterday.

"Since this went into effect today at 00:01 in Damascus, we have seen an overall decrease in violence in these

jihadist militants allied to the rebels had disrupted a plan for a temporary truce that was to take effect on Tuesday.

Meanwhile, activists reported that government warplanes had carried out more than 20 air strikes in the rebel-held eastern Ghouta outside Damascus, after the regime of calm declared by the government around the capital on Saturday expired.

A surge in fighting in Aleppo in the past two weeks has killed almost 300 people.

Aid agencies say Aleppo is on the brink of

areas," spokesman Mark Toner said.

Once a nationwide "cessation of hostilities" is again in place, the United States and United Nations hope the warring parties will return to peace talks.

Kerry has warned that if Assad's regime does not agree to begin a political transition away from his rule by August 1, it may face unspecified "repercussions." Reports in Washington suggest that this may mean the United States or its allies in the region are stepping up military supplies and training for the rebels.