Syria's besieged enclave of eastern Aleppo has no anesthetists and only six intensive care beds after two hospitals were disabled by airstrikes overnight, a doctor from the Syrian American Medical Society said on Wednesday.

Russian or Syrian warplanes knocked a major Aleppo hospital out of service on Wednesday, hospital workers said, and ground forces intensified their assault on the city's besieged rebel sector, in a battle that has become a potentially decisive turning point in the civil war.

Shelling damaged at least one other hospital and a bakery, killing six residents lining up for bread under a siege that has trapped 250,000 people with food running out.