Four medics killed in strike on clinic near Aleppo

Four medics were killed and a nurse critically wounded when an airstrike hit a clinic in a village near Syria's second city Aleppo late Tuesday, just days after dozens of aid workers were killed.

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.

The attack comes a day after all aid convoys to Syria were temporarily suspended after a deadly airstrike on Monday killed 12 aid workers and drivers, and destroyed at least 18 trucks carrying aid to Aleppo.

It's "a very, very dark day... for humanitarians across the world," Jens Laerke, spokesman for the UN humanitarian aid agency, OCHA, said.

An infuriated United Nations warned Monday night's attack could amount to a war crime.

In a statement late on Tuesday, the Syrian Civil Defence confirmed that Russian and regime warplanes were behind the "deliberate attacks" that targeted the convoy.

But Russia has denied its aircraft or those of its Syrian government allies were involved in the incident. The strike appeared to deal a fatal blow to Syria's fragile week-old ceasefire.