As many as 11 EU countries are rebelling against EU diktats on migration, in the face of growing concerns about illegal migration.
Countries including France, Slovakia, Sweden and Germany have re-instated border restrictions including identity vetting, passport checks, police interviews, static checkpoints and vehicle inspections.
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Such restrictions on movement were abandoned many years ago as part of the Schengen Treaty.
But they are now viewed by a number of countries as being essential to stop "infiltration" by terrorists posing as migrants.
Peter Szijjarto, the foreign minister of Hungary, issued a warning to the EU over its migration policy.
He said: "If Brussels does not change its migration policy, we could find ourselves where we do not want to be: in an era of Europe torn apart by old borders."
This came after Italy escalated its own internal border checks with neighbouring Slovenia as part of an attempt to reduce the "increased threat of violence within the EU", which the country believes has escalated since the outbreak of the Israel-Hamas war.
Italy said the changes were necessary as a result of the growing risk of terrorists arriving due to "constant migratory pressure from land and sea".
In the wake of Italy's border checks, Slovenia did the same with its borders with Hungary and Croatia, claiming it faces the same issues as Italy.
Slovenia also claimed to be facing "threats to public order and internal security".
Meanwhile, Sweden has warned it is conducted checks at all its border points to combat terrorism.
Andrej Plenkovic, the prime minister of Croatia, backed the move by other European countries.
He said: "The EU is surrounded by a series of very big crises... bigger than any time in the past 30 years.
"We have Putin's aggression against Ukraine, Hamas's attack on Israel, all this in the context of intensified flows of illegal migration."