French Interior Minister Bernard Cazeneuve has sharply criticised Belgium's decision to impose checks along its border with France to stop people coming from the "Jungle" refugee camp in Calais.
"This decision is a strange one, just as is its motivation," Cazeneuve said in Brussels before an EU meeting with his counterparts.
Belgium has launched a huge operation to monitor three border crossings and surrounding sand dunes in the De Panne region bordering France.
Belgian Interior Minister Jan Jambon moved nearly 300 extra police to the Flemish coast to patrol its border with France and the area around the port of Zeebrugge on Tuesday.
This was in anticipation of a decision by France to demolish the "Jungle" refugee camp in Calais, a northern French port city near the Channel Tunnel rail link which leads to Britain.
"We were never warned," France's Cazeneuve said, describing the decision as "odd."
Belgian Interior Minister Jan Jambon said most of the refugees in Calais wanted to get to Britain and failing that, they would use Belgium as a transit route via the port of Zeebrugge
"Any claim that this [operation] could cause an increase in the flow of migrants to the Belgian border does not correspond to reality," Cazeneuve said.
The European Commission, the EU executive, said on Thursday that it was seeking further explanations from Belgium about the additional border controls it is introducing.