Swiss border guards have tightened controls at key crossings to prevent anti-globalisation protesters from reaching the Italian city of Genoa, ahead of the G8 summit, which kicks off on Friday.
Seven German tour buses heading for Genoa, as well as many cars, were stopped at the border crossing with Basel on Thursday, and six passengers were prevented from continuing their journey.
The vehicles were delayed for several hours as German and Swiss border guards using dogs methodically searched their luggage for weapons and checked identities.
According to the German customs department, the six people who were prevented from leaving Germany are known to have committed acts of violence during demonstrations.
The move is part of wider Swiss efforts to assist Italy in keeping anti-globalisation protesters out of the country during the G8 summit.
Protesters have resorted to demonstrations at Swiss border crossings to vent their anger at not being able to move freely. On Wednesday night, around 150 dancing anti-globalisation demonstrators blocked Switzerland's southernmost border post at Chiasso for three hours.
It was second time border traffic had been disrupted in the past 48 hours. Wednesday unauthorised protest remained peaceful, and the 50 riot police present did not intervene. Cross-border traffic resumed at 2300.
Those protesters were demonstrating in support four Germans who were denied entry into Italy. The four, part of a group heading to Genoa for the G8 summit, were stopped from entering Italy by the authorities, who said they did not have appropriate identification papers.
Italy has temporarily suspended the Schengen agreement, which guarantees the free movement of people throughout much of the European Union. Italian police hope this will help to avoid a repeat of violent demonstrations, which have taken place at major summits around the world over the past few years.
A demonstration near Chiasso late on Monday led to clashes with the police after protesters attempted to block trains crossing the border.
Switzerland announced earlier this week that it would exchange information on known anti-globalisation protesters with the Italian authorities. The move led to criticism that this was an infringement of basic liberties, and a violation of data protection laws.
Austria and Germany have joined Switzerland in imposing tighter border controls ahead of the G8 summit.
swissinfo with agencies