Far-left groups represent the most serious threat to Swiss security, according to a government report on extremism released on Thursday.
But no extremist group – from the Left, Right or abroad – poses an immediate threat to the safety of the country.
The Federal Police Office report assesses extremism since 1992, the year of the first government report on the question.
It concludes that the activities of far-left groups pose a “serious” risk for the security of Switzerland “which should not be underestimated”.
Since 1992, incidents involving the many extreme Left factions have risen sharply, along with a rise in violence and group membership.
The report said around 2,000 militants now belonged to these groups.
The report’s authors say solutions are elusive because leftist extremists don’t negotiate and are becoming increasingly aggressive. They are particularly active in large cities like Zurich and Basel, the report added.
The threat of rightwing extremists is waning in comparison. These groups only occasionally flout law and order.
But compared with the 1990s, rightwing extremists are increasingly visible and publicity-seeking. Membership is growing, and is estimated at 1,000 people.
The report makes a connection between alcohol and violence among younger members of the extreme Right. When these groups drink, said the report, "almost nothing stops the vandalism or racist acts".
The climate surrounding foreign, political or religious extremist groups is described by the report’s authors as "calm, but tense" .
Certain groups, including Kurds and Tamils, could become a threat to Switzerland in the event of a destabilising change in their native countries, they argue.
“The potential for mobilisation of foreign extremists remains,” the report said.
It notes that Islamist groups tend to observe the law. Some use Switzerland as a base for organising and recruiting members, but these groups are not believed to be engaged in terrorist activities.
The report says the battle against terrorism must be stepped up, a subject the federal government will consider this autumn.
The report faults Swiss law for its inability to fight hooligans.
The government has taken preventive measures, toughening the law on weapons, and cracking down on racism.
But current legislation says little about hooliganism and propaganda inciting violence.
Critics say extremists could cause trouble at the 2008 European football championships, to be jointly organised by Switzerland and neighbouring Austria.
A new law, currently being drafted, foresees travel bans for violent sports fans as well as preventive detention for known hooligans.
The Federal Police Office has said detention would only be used as a last resort.
Officials have called for closer international police cooperation ahead of Euro 2008.
swissinfo with agencies
According to the Federal Police Office report:
The extreme Left in Switzerland counts some 2,000 militants, who are well organised and urbanised.
Since 1992, incidents involving extreme Left factions have risen sharply.
The extreme Right numbers about 1,000 people.