Four medics were killed and a nurse critically wounded when an air strike hit a clinic in a village near Syria's second city Aleppo late Tuesday, the aid group that runs it said.

The four staff of the Union of Syrian Medical Relief Organisations were in two ambulances that had been called to the clinic to take some patients for more specialised treatment, the group said.

The clinic in the village of Khan Tuman was completely levelled and more dead were feared to be buried under the rubble, the group added.