To comply with the new Swedish rules, passengers had to show identification Monday to board trains departing from Copenhagen Airport in Denmark to Sweden across a bridge-and-tunnel link.
It is the latest move by a European Union country to suspend an agreement to keep internal borders open, AP reported.
Danish officials have criticized the move and suggested Sweden should pay for the cost of the ID checks.
The Swedish government decided to tighten border controls after 160,000 people applied for asylum in Sweden last year — the highest number in Europe except for Germany. Most of them were from Syria, Iraq and Afghanistan.