The Swiss authorities have barred around 100 people from travelling to the World Economic Forum in Davos next month.
The bans have been imposed on foreign activists known to have committed, or believed to be preparing, "acts of violence".
Jean-Luc Vez, the head of the Swiss Federal Police Office, told the "NZZ am Sonntag" newspaper that Switzerland was bracing for a difficult year in 2003.
Topping his list of concerns is the Davos economic forum - which attracts many of the world's political and business leaders - as well as the G-8 summit, which will take place in Evian, on the French side of Lake Geneva.
"[I] fear that 2003 will not be an easy or peaceful year," Vez told the newspaper.
"[Attacks] in Bali and Kenya have shown that international terrorism can strike anywhere," he said.
"And should there be a war in Iraq, this danger will not diminish."
Vez said that other countries - which have provided information about known agitators - had helped Switzerland prepare a crackdown on anti-globalisation protesters.
Threats against internal security
Swiss laws allow the authorities to bar individuals who could "endanger internal security".
Vez said he believed the majority of protesters had peaceful intentions, but warned that those who committed acts of violence would be identified and isolated.
Along with Davos, Switzerland will face a significant security headache during the G-8 meeting in June.
While not directly on Swiss soil, the high-powered Evian summit will involve Swiss cantons surrounding Lake Geneva.
Vez said a key question still to be resolved is the issue of security arrangements between Geneva airport and the conference venue.
French police and armed forces may be required to operate in Swiss airspace and on Swiss territory - opening-up questions of sovereignty.
One solution may be the signing of a special bilateral agreement dealing with cross-border security operations.
Swiss media have questioned whether this would include the electronic monitoring of Swiss citizens.
swissinfo with agencies
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