Croatia, which last year saw hundreds of thousands of migrants pass through on their way to Western Europe, has erected metal barriers on a bridge at the border with Serbia to prevent illegal entry.
The interior ministry said in a statement it had set up the barriers on the bridge over the Danube River at the Batina-Bezdan border crossing. "The technical barriers could be activated to completely close the bridge," it said.
Last year some 650,000 migrants, mainly Syrians, Afghans and Iraqis, crossed Croatia on their way to the European Union's visa-free Schengen zone.
Other states in the region, including Hungary and Slovenia, have erected border fences. In March, Macedonia, Serbia, Croatia and Slovenia closed their borders to refugees, forcing them to seek alternative routes or pay smugglers.