The United States says it is working on specific initiatives to de-escalate fighting in Syria and revive a nationwide cessation of hostilities. A priority is to stop bloodshed in Aleppo where more than 200 people have died in a week of government air strikes and rebel shelling. The US wants Russia to put pressure on the Syrian government to stop what it says is an indiscriminate bombardment. But Russia insists the air raids on Aleppo are targeting terrorist groups. US Secretary of State John Kerry dismissed Russian and Syrian government claims that the Aleppo strikes were targeting the al-Nusra Front, a jihadist force that is not party to a ceasefire.

Mr Kerry is in Geneva on Sunday to discuss the situation with the the UN envoy to Syria, Staffan de Mistura, and the foreign ministers of Jordan and Saudi Arabia. He has expressed his deep concern about the deteriorating situation in Aleppo, with more government air strikes on Saturday reported to have killed at least four people with many more wounded, mostly in the neighbourhood of Bab al-Nairab.

The US secretary of state blames the government of President Bashar al-Assad of worsening the conflict by predominantly targeting civilians. The US argues that such attacks are direct violations of the cessation of hostilities which came into effect two months ago and must stop immediately. In telephone calls to Mr de Mistura and the Syrian opposition's General Co-ordinator for the High Negotiations Committee, Riyad Hijab, Mr Kerry said efforts to secure peace must take place in Aleppo as well as in the areas of Latakia and Eastern Ghouta. State department spokesman John Kirby said work was taking place to defuse tensions and the hope was that "tangible progress" would be made soon.

Mr Kirby said diplomatic pressure was being put on Russia to stop regime violations, especially its indiscriminate aerial attacks on Aleppo. He said that Mr Kerry would continue working through the International Syria Support Group to implement a cessation of hostilities nationwide and to stop "regime obstruction of the delivery of humanitarian relief to all areas in need and to make concrete progress towards a political transition". A truce was called in February between President Assad's forces and rebels in Syria but it has broken down in recent months, especially in the divided and besieged Aleppo.

The Syrian army says the truce is being maintained in all of Syria except in Aleppo. A new round of UN-backed peace talks is set to start on 10 May in Geneva. Large parts of Aleppo have been destroyed and its infrastructure has been severely damaged, leaving civilians without water and electricity for months.