Organizers of this weekend's Canadian Grand Prix have called off a scheduled "open house" day.
The promoters of the Montreal race had planned to allow spectators to attend the Circuit Gilles Villeneuve and tour the F1 pitlane for free on Thursday.
La Presse newspaper said the open day has taken place since the early 90s, with 12,000 taking advantage last year.
But according to the Canadian Press, it has been called off in 2012 due to "security concerns", amid threats made by protesting university students and internet terrorists.
"Considering the various disruption threats made public recently, the free admission and the naturally open character of the open house day revealed some risks that we could not ignore," said promoter Francois Dumontier.
"We wish to express our sincere apologies to the F1 fans and, among them, a good share of our spectators who appreciate this annual gathering with the world championship teams," he added.
Despite the cancellation, Dumontier insisted Montreal is safe for race-goers.
"We cannot deny that something is happening in Montreal," he told La Presse, "but what is conveyed in the foreign media is always the same -- stunning images of petrol bombs and clashes with police.
"I am trying to reassure people who are asking me questions about it. There are F1 people who arrived a few days ago and they have said nothing to me about the situation."
He admitted to having ramped up security.
"We will not divulge any details," Dumontier is quoted by the Times, "but we already have a rather elaborate plan.
"We increased security, reviewed certain points that might have been more vulnerable and, over several weeks, have been working closely with the police. We're ready for several contingencies."
