At least 20 people, most of them rebel fighters, have been killed and dozens injured in a bombing near Syria's border with Turkey, activists say.

The attack reportedly occurred during a change of guard at the rebel-controlled Atmeh crossing, in Idlib province.

It was not immediately clear whether the blast was caused by a suicide bomber or a remote-controlled device.

But a news agency linked to so-called Islamic State (IS) said a suicide car bombing had targeted a rebel convoy.

Photographs and video footage purportedly of the aftermath of the attack showed the bloodied bodies of more than 20 men, some of them wearing camouflage trousers.