At least 12 civilians including five children have been killed in fresh air strikes on the besieged Syrian city of Aleppo, it has been reported.

The attacks occurred hours after Western powers threatened Syria and Russia with economic sanctions unless they stop bombing the rebel-held city

More on war in Syria

The Britain-based Syrian Observatory for Human Rights said the five children were killed in the Marjeh district of east Aleppo.

US Secretary of State John Kerry defined the situation in the city as "the largest of humanitarian disasters". UK Foreign Secretary Boris Johnson claimed that "crimes against humanity" were occurring on a daily basis in the city.

The US and Russia reached a ceasefire in September. However, the truce collapsed shortly after. Syrian government forces, backed by Russian air strikes, have intensified their bombardment of rebel-held areas in Aleppo since.

Rights groups and aid organisations including Save the Children and Oxfam have called for a 72-hour-long ceasefire to allow evacuations and aid deliveries.

However, Syrian President Bashar al-Assad claimed government forces will continue to carry out air strikes in Aleppo to "keep cleaning this area".

Earlier in October, barrel bombs struck a hospital in Aleppo, days after it was shelled by missiles alongside the second-largest hospital in the area.

Syria Russia Isis Islamic State