Of the 31 countries receiving higher terrorism risk ratings than last year, 48% are in Western Europe. Among them, the Netherlands, Germany, Belgium and Denmark have all been marked as higher risk because of increased extremist activity in their domestic Muslim populations. The most recent manifestation of this was the murder of film-maker Theo Van Gogh by a Dutch Moroccan Islamic extremist.
Fears that Islamic extremists might stage attacks to try to influence the UK general election on 5 May also reinforced the UK's risk rating, which remains unchanged from last year.
The terrorism map shows that participation in the US-led Iraq coalition has increased terrorism risk in countries such as Australia, Poland and Estonia.