By Stephanie Nebehay
GENEVA (Reuters) - New border controls in the western Balkans are leaving thousands in limbo as winter sets in, aid agencies said on Friday.
Balkan countries have begun filtering the flow of migrants, granting passage to those fleeing conflict in the Middle East and Afghanistan but turning back others from Africa and Asia, the United Nations and Reuters witnesses said on Thursday.
The measures by Macedonia, Slovenia and other states are creating tension at border crossings and leaving some families stranded, the U.N. refugee and children's agencies and the International Organization for Migration (IOM) said in a joint statement.
"There is urgent need to put in place additional reception capacity at the points of entry," the spokesman for the U.N. High Commissioner for Refugees (UNHCR), Adrian Edwards, told a news briefing in Geneva.
More than 4,000 refugees and migrants are flowing into Europe each day, he said.
"It is a decision made in urgency, out of desperation, they have to abandon their homes, their families. That is something that is not affected by the seasons," Edwards said. "There has to be a means to manage this situation."
Slovenia has started imposing selection criteria, leading to concerns that migrants might change routes via Bulgaria, where conditions are even more precarious, IOM spokesman Joel Millman said.
"Refugee and migrant children are amongst the worst off," said U.N. Children's Fund spokeswoman Sarah Crowe. People younger than 18 now account for about a third of new arrivals in Gevgelija, Macedonia, up from one in 10 in June, she added.
(Reporting by Stephanie Nebehay; Editing by Andrew Heavens)