Moscow has warned of "serious consequences" after Turkey shot down a Russian fighter jet taking part in air strikes on Syria.

Russia said the Su-24 was one of around 50 aircraft taking part in its campaign against what Moscow describes as terrorist groups in Syria. It accused Turkey of protecting Islamic State (IS) militants.

But Turkey said the Russian jet had violated its airspace, and had been repeatedly warned to alter its course.

The incident shows the potential for a spill-over of the Syrian conflict across the borders of its neighbours, exacerbated by the number of competing nations now in action in Syrian airspace, as Jonathan Marcus explains.

Video produced by Michael Hirst