A massive security operation is under way ahead of the opening of the Winter Olympic Games in Turin, northern Italy.
Protesters disrupted the progress of the Olympic flame
Authorities are spending more than $100m (£57m) on security, with 15,000 police officers being deployed.
There will be a no-fly zone over the city as 15 heads of state attend Friday's opening ceremony.
On Thursday, the Olympic flame was diverted in Turin to avoid protests over a planned local high-speed rail link and over spending on the Games.
An Italian government statement said it was focusing on two issues - the possible internal repercussions from Islamic protests around the world and the growing aggressiveness of Italian anarchists and subversive groups.
Two of Nato's surveillance aircraft will be enforcing the no-fly ban over Turin during the opening ceremony.
The Italian government has repeatedly warned of a threat from protesters seeking an international spotlight.
The torch relay carrying the Olympic flame around Italy has been disrupted several times during its two-month trip.
On Thursday, police had to change the route in Turin to avoid hundreds of people protesting against the rail link.
Protesters say that tunnelling for the railway in the Susa valley, where some of the events will be held, will ruin the environment and release asbestos and uranium into the atmosphere.
"These are dirty Games because they have spent huge amounts of money and we don't know what use it will be in the future," an unnamed protester told Reuters.