The tug of war over border controls in Croatia and Serbia has intensified.
Croatia has banned all Serbian registered vehicles from entering its territory.
Seen as retribution, the block comes hours after Serbia placed an embargo on Croatian trucks and goods.
Immediately before this, a Serbian ultimatum had expired, which had warned its neighbour to lift a two-day-long embargo on Serb trucks, or face consequences.
Croatia says its initial closure of most border points with Serbia was the only option as 44,000 migrants who had been turned away from Hungary flocked to the country in the past week (up to September 23, 2015).
Speaking at the midnight ultimatum expired, Serbian Interior Minister Nebojsa Stefanovic said his country was willing to work towards a solution.
“Unfortunately, there is very little that Serbia can do alone,” said the Interior Minister. “For this, the will of both countries is needed. We are ready at any moment to solve this.”