Denmark has imposed controls on its southern frontier with Germany in a move that is intended to stem the flow of migrants but will also deepen concerns about Europe's fraying commitment to the free movement of people.
Lars Lokke Rasmussen, Danish prime minister, said the decision was prompted by Sweden's move hours earlier to introduce identity checks for all passengers arriving by train, bus or ferry from Denmark.
"The new Swedish requirement for ID checks poses a serious risk of a large number of asylum seekers accumulating in a short time, for example in and around Copenhagen, threatening public order and safety. We do not want this," he said at a hastily called press conference on Monday.
The Danish controls are temporary and will last for the next 10 days but can be extended. Distinct from the Swedish measures, they will involve random checks and will not automatically require all cars and passengers crossing from Germany to show their passports. Mr Rasmussen said Angela Merkel, German chancellor, and the European Commission had been notified.
Nonetheless, the new controls — particularly the Swedish checks on passengers crossing the Oresund strait between Copenhagen and Malmo — illustrated how the migrant crisis is pushing up barriers and stirring tensions between even the closest European neighbours. They were denounced by politicians and commuters in the region.