Zurich police have rejected Danish accusations that they failed to warn them ahead of a European football match that Swiss fans presented a security risk.
More than 100 Swiss supporters were detained on Thursday after skirmishes with police before a Uefa Cup game between Bröndby IF and FC Zurich.
Danish police spokesman Arne Wissing said on Friday that Zurich police had not responded to a request for information about hooligans travelling to the Bröndby game despite this being a distinct possibility.
Three officers were slightly injured in the clashes – 90 minutes before the match was to begin – near the suburban stadium in Bröndby. One Swiss fan was also injured.
Several officers fired warning shots into the air, said chief constable Joern Bro. The Swiss fans were escorted by nine police officers on a train to Bröndby where some of them assaulted police at the station.
The fans hurled stones and empty bottles and used their belts as weapons.
"It was so violent that the officers had to flee the train station and drew their guns and shot in the air," Bro told Denmark's TV2 channel.
The incident started after officers tried to arrest a fan writing graffiti on the train, Bro said.
The supporters were also involved in some minor brawls after arriving in the Danish capital Copenhagen earlier in the day, officers said.
Zurich city police have reacted, telling swissinfo they did inform the Danes before the match about potential risks.
"We gave them complete, correct and detailed information," said spokeswoman Susanna Birrer. "We are not responsible for what people do with that information afterwards."
The Danish police were told 400-500 Swiss fans were expected to make the trip to Bröndby, with around 50 potential troublemakers among them.
"We warned the Danes these potential hooligans could become aggressive if provoked," Birrer told swissinfo. "They tend to drink a lot and you have to consider that they might be carrying devices such as flares with them."
She added that what happened could not be foreseen since it neither involved Bröndby fans nor took place within the stadium. "We considered this match to be a low risk," she said.
The Swiss government has been taking hooliganism seriously in the lead-up to the 2008 European football championships which will take place in Switzerland and Austria.
Travel restrictions, preventive detention and the banning of troublemakers are among the proposals to be presented to parliament. A database of known hooligans is also being set up.
The fear that hooliganism could disrupt the championships was brought home to policymakers earlier this year after clashes between supporters of Basel and Zurich's other club, Grasshoppers.
The authorities must now clarify whether the proposed anti-hooligan legislation can be integrated into federal law or adopted at the cantonal level.
Bröndby won the game 2-0.
swissinfo with agencies
Anti-hooligan measures proposed by the Swiss government ahead of Euro 2008 include:
Police powers to seize and confiscate extremist propaganda material;
National database of hooligans;
Exclusion of troublemakers from sporting zones during matches;
Obliging known hooligans to present themselves at police stations;
Preventive detention (maximum 24 hours) as a last resort.
Four of the Swiss fans arrested in Copenhagen are facing criminal charges.
In Switzerland, 400 people have been banned from football stadiums.
The number of violent spectators in Switzerland is estimated at around 600.
The cost of security measures for Euro 2008 is estimated at SFr53 million ($42 million).