VRSKA CUKA, Serbia (Reuters) - Across south-east Europe, governments are throwing up barriers to keep out migrants arriving via Turkey, but numbers are still creeping up as rougher seas lead more to try this Balkan route rather than risk a Mediterranean crossing.

Migrants, who said they were from Syria, are being apprehended by the Serbian border police for having illegally entered the country from Macedonia, near the town of Presevo some 383 km (238 miles) from capital Belgrade, Serbia, April 29, 2015. REUTERS/Marko Djurica

Since July, Serbian border guards have stopped more than 10,000 migrants attempting to cross from Bulgaria and Macedonia, but charities have reported sharply lengthening queues for food in Serbian refugee camps over recent days.

Last autumn, hundreds of thousands of migrants trekked up from Turkey through the rocky Balkan peninsula, hoping to enter the European Union’s passport-free Schengen zone by crossing into Hungary. Many were refugees fleeing conflicts in countries such as Syria, Iraq and Afghanistan.

Numbers are lower this year, partly because of an agreement under which the EU pays Turkey to house Syrian refugees, and partly because border fences along the route have made the journey harder. But the trickle is growing, and more than 100,000 have reached the Balkans so far this year.

Border patrols deterred most of the migrants, Serbian defense ministry spokesman Jovan Krivokapic said, but 960 illegal migrants had recently been caught and taken to reception centers.

“Over the past two weeks we have seen increasing pressure from the Bulgarian side of the border,” he said. “Groups of up to 50 people are taking advantage of good weather to enter using wooded areas and rugged mountain passes.”

The patrols, equipped with all-terrain vehicles, armored personnel carriers and thermal vision equipment, range along the 460 km (285-mile) boundary with Macedonia and Bulgaria. Hungarian officials are helping them, and they are set to be joined by Austrian and French reinforcements.

Only a trickle get across the fenced-off border into Hungary, and that number may fall further after that country holds a referendum on Sunday on whether to accept proposed EU mandatory migrant quotas, after which Budapest may fully seal its borders.

Some 7,000 migrants are currently stranded in camps throughout Serbia, up from 4,000 in July, and tensions are running high. Many refugees make repeated attempts to cross international borders, often with smugglers’ help.

Aid workers at a reception center by Belgrade’s Sava River said lines of migrants queuing for breakfast had doubled in length overnight on Friday morning.

“Once I went 15 km, the police caught us and sent us back,” said one Pakistani migrant of his repeated attempts to sneak into Hungary. “I tried three days ago and walked for 5 km when police caught us and sent us back.”