The checks were conducted on trains and vehicles crossing the Oresund Bridge over the narrow waterway that separates Copenhagen, Denmark's largest city, and Malmo, Sweden's third-largest city. Checks were also carried out at ferry ports.
Police spokesman Jens Jespersen told The Associated Press that officers at the Oresund Bridge vehicle checkpoint had "a particular focus on cross-border crime involving explosives, weapons and drugs." He also said authorities were stopping cars to have "a peak at who is inside."
"It gives us a pretty good picture of who is coming over," he said.
For years, Danes and Swedes have been able to cross without needing a passport. Now a passport is needed for Swedes entering Denmark - at least for the next six months.
That requirement and the checkpoints come after violence that includes 13 explosions in Copenhagen since February, as well as a shooting in June that killed two Swedish citizens.
The spiraling violence is believed to be gang related, stemming from disputes over drugs, money, protection and retaliation. An estimated 200 people in Malmo belong to about a dozen gangs.
On Saturday, a shooting in Malmo killed a 15-year-old boy and critically wounded another. Police said the teenagers who were shot were well-known to authorities in Malmo and officials vowed to crack down even further on organized crime. No one has been arrested.
Lilian Gustavsson, a 67-year-old Swedish woman who was about to embark on the train to Malmo from Copenhagen's international airport, said she understood why the Danes were carrying out the checks.
"I believe this will mean a little travel delay for everyone," she said. "I fear we might get stuck, but better that than having criminals crossing."
As part of Monday's checks, all vehicles coming from Sweden on the Orseund Bridge were led to a rest area on the Danish side. They then went through a large white tent where officers checked the driver, passengers and the car. Police scanned vehicle license plates, Jespersen said, "so if a (vehicle) is known in the system, we can pull it aside."
During the roughly four-hour check Monday, no one was pulled aside, he said. He declined to give details as to when police would carry out further checks but said "a good guess would be two or three times a week."
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