By Stephanie Nebehay and Marjan Ognenovski GENEVA/GEVGELIJA, Macedonia (Reuters) – New border controls in the western Balkans are leaving migrants stranded behind barbed wire as temperatures start to plunge, and aid agencies warned on Friday that the clampdown would lead to a rise in smuggling. Balkan countries have begun filtering the flow of migrants, granting passage to those fleeing conflict in the Middle East and Afghanistan, but turning back thousands from Africa and Asia. The measures by Macedonia, Serbia and other states are creating tension at border crossings and leaving some families stranded without adequate shelter, the U.N. refugee and children's agencies and the International Organization for Migration (IOM) said in a joint statement.

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