Turkish President Tayyip Erdogan said on Monday developments in Syria's northwestern region of Idlib had become "unmanageable", after Ankara said Syrian shelling killed five of its soldiers there.

Earlier on Monday, Erdogan said Turkey was retaliating for the attacks, adding that had told Russia, which backs Syrian President Bashar al-Assad, to "stand aside".

Speaking in Kiev, Erdogan said there were close to 1 million people in Idlib marching towards Turkish borders as a result of a Russian-backed Syrian government offensive.