The Swiss authorities have issued entry bans against 300 anti-globalisation activists in what they say is a bid to avert violent protests against the forthcoming World Economic Forum meeting in Davos.
The justice minister, Ruth Metzler, said "there are people who are intent on going on the rampage in Davos. We're determined not to let these people into Switzerland."
Metzler said the entry ban applied to people "who have used force and would presumably use it again".
A justice ministry spokesman refused to say who was on the list, but told swissinfo that those on it would be turned back at the border if they tried to enter Switzerland.
The authorities have imposed an official ban on all demonstrations in Davos during the meeting, which runs from January 25 to 30. They have said they will screen all trains and vehicles to keep protestors away from the canton Graubünden resort.
Six hundred soldiers are strengthening the local police forces, and hospitals in the area are reportedly on a state of alert.
About 3,200 people, including more than 30 heads of state and prime ministers, are due to attend the annual event.
The Davos meeting, now in its 31st year, was long enjoyed by political and business leaders for its laid-back atmosphere which allowed the world's elite to mingle freely and strike deals far from the pressures of life back home.
But all that changed last year when anti-globalisation protesters, encouraged by their success in halting a December 1999 World Trade Organization meeting in Seattle, laid siege to the village.
The authorities fear this year may be even worse. Masked protesters gave a press conference earlier this month and pledged they would reach Davos despite police attempts to keep them at bay.
The United States State Department on Friday issued a warning to Americans about possible "disorderly and violent" demonstrations and advised people to "exercise caution and consider deferring travel to Davos".
The department warned that there was a risk of terrorist attacks on the village, and placed Switzerland on a danger scale equivalent to trouble spots such as East Timor, the Philippines or Kyrgyzstan.
There has been angry reaction from Swiss politicians and the tourist industry over the warning. The Radical Party president, Franz Steinegger, described it as "totally disproportionate".
"[Davos] is hardly going to be worse than Seattle," he said. The Swiss People's Party president Ueli Maurer went further, accusing the US of "incredible arrogance".
Jürg Schmid, tourism director for Davos, said that the State Department warning would actively damage the village's image as a holiday destination.
The authorities in canton Graubünden have said that no special measures will be taken to protect Americans in particular. They said that existing security measures are completely sufficient to ensure the safety of the forum participants and other people visiting Davos.
swissinfo with agencies