BELGRADE (Reuters) - Around 100,000 migrants from Middle East, Asia and Africa have passed through Serbia so far in 2016 despite the closure of the so-called 'Balkan route' which hundreds of thousands used last year to reach Western Europe, a Serbian minister said.

"This means that the Balkan route still exists and people are now moving to European Union countries with greater and greater difficulties," the Tanjug news agency quoted Aleksandar Vulin, minister in charge of social welfare, as saying.

More than 650,000 people, many of them fleeing war and poverty in the Middle East and elsewhere, passed through non-EU Serbia last year on their way to the European Union.

This route was largely shut down in March after a series of border closures by EU states.

Last month Hungary, Serbia's northern neighbor and an EU member, adopted a law that allows police to send back illegal migrants detained within eight kilometers (five miles) from its razor wire-fenced southern frontier with Serbia.

Hungary has also limited the number of daily admissions into the transit zone to a maximum of 30. The move created a bottleneck, with migrants creating makeshift camps near the transit zones between the two countries.

According to United Nations refugee agency (UNHCR) on Friday there were around 1,300 migrants in open air centers and makeshift camps near Hungarian border and a total of around 2,300 in Serbia as a whole.

"Close to 800 asylum seekers are waiting in the open on Serbian territory outside the Hungarian 'transit zone' near Horgos border crossing, where overall conditions, particularly lack of shelter, health and sanitation represent major challenges," it said in a statement.

Over past three months a majority of migrants who entered Serbia came across Bulgarian border after an arduous journey by land from Turkey, Vulin said.

He said Serbia would not allow its border to become a bottleneck where migrants would amass after EU states closed their borders.

"Because of closed borders Serbia may find itself in a problem, Serbia will not allow that," he said without specifying whether Belgrade would also seal its borders.