Switzerland and its European neighbours are tightening up border controls ahead of the Group of Eight summit, which opens in the Italian city of Genoa on Friday.
Fears over security have already led Italy to suspend the Schengen agreement on open borders and impose strict controls on people entering the country from other parts of Europe.
Swiss police officials said border controls had been stepped up in response to moves by the Italian authorities to tighten security. They said the two countries were exchanging information to try to prevent disruptions of the summit.
On Monday, around 100 anti-globalisation protestors attempted to block an inter-city train from crossing the Swiss border into Italy. Demonstrators from Switzerland, Germany, Italy and the United States marched onto the railway tracks at Chiasso on the Swiss-Italian border.
In another sign of increasing tension, a letter bomb exploded in Genoa. Police blamed the action on extremists intent on disrupting the G8 summit.
German border guards and police said on Monday that they had stepped up controls on passengers travelling beyond the country's southern border. They said extra precautions were now being taken on the borders with Switzerland and Austria.
Jürg Prufer, head of communications at the Swiss Federal Police Office, said the tighter controls were aimed at people displaying a tendency towards violence and known opponents of globalisation.
"It's clear that when people are violent, they will be prevented from entering Switzerland," he told swissinfo.
But Prufer made it clear that most people would have no problems passing through the country. "We expect several hundred people to pass through Switzerland in connection with this event. But as long as they are not violent they will be allowed through."
A spokesman for the federal border guards, Martin Bigler, said Switzerland was anxious to avoid problems at its southern borders at the height of the holiday season. But he said holidaymakers venturing into Italy were bound to be affected by delays as increased checks were carried out.
More than 100 Swiss opponents of globalisation are expected to travel to Genoa.
swissinfo with agencies