Greek troops and riot police are on high alert along the land border between Greece and Turkey, the main flashpoint in an escalating row between the European Union and Ankara over how to deal with a new wave of refugees and migrantsSome 10,000 refugees and migrants have been trying to breach the border since Turkey said last Thursday it would no longer uphold a 2016 accord with the EU to keep refugees and migrants on its territory in return for billions of euros in aid.