Russia has warned the US against carrying out any attacks on Syrian government forces, claiming there would be repercussions across the Middle East.

Russia and Iran will be guilty of war crimes if they do not put pressure on Syrian President Bashar Assad to stop escalating violence in the country, says France's foreign minister.

Fighters from the Islamic State group have launched a new offensive on the northern Syrian town of Kobani after shelling the area from their positions nearby, activists said.