Serbia has begun allowing only Syrian, Iraqi and Afghan refugees through the country on the main migrant route to northern Europe, a UN refugee agency spokeswoman said Thursday.

"Since yesterday afternoon Serbian authorities allow into the country only refugees from Afghanistan, Syria and Iraq," when they have documents to prove it, said spokeswoman Melita Sunjic.

She said Macedonia was also limiting refugees from certain countries including Liberia, Morocco, Pakistan, Sri Lanka and Sudan.