A report that Norway's bomb and gun rampage may be the work of a far-right militant confronts Europe with the possibility that a new paramilitary threat is emerging, a decade after al Qaeda's Sept. 11 attacks.
One analyst called the attacks possibly Europe's "Oklahoma City" moment, a reference to American right-wing militant Timothy McVeigh who detonated a truck bomb at a federal building in Oklahoma City in 1995, killing 168 people.
Police forces in many western European countries worry about rising far-right sentiment, fuelled by a toxic mix of anti-Muslim and anti-immigrant bigotry and increasing economic hardship.
But violence, while sometimes fatal, has rarely escalated beyond group thuggery and the use of knives.
That may have changed in Oslo and on the holiday island of Utoeya on Friday. Seven people were killed in a bombing in the capital -- Western Europe's worst since the 2005 London al Qaeda-linked suicide attacks that killed 52 people -- and at least 10 in a shooting rampage by a lake.
Independent Norwegian television TV2 reported on Saturday that the Norwegian man detained after the attacks had links to right-wing extremism.
Police were searching a flat in west Oslo where he lived, TV2 said.
"If true this would be pretty significant - such a far-right attack in Europe, and certainly Scandinavia, would be unprecedented," said Hagai Segal, a security specialist at New York University in London.
"It would be the European/Scandinavian equivalent of Oklahoma City - an attack by a individual (with extremist anti-government views, linked to certain groups) aimed at the government by attacking its buildings/institutions."
"The next key question is whether he was acting alone, or whether he is part of a group."
A report by European police agency Europol on security in 2010 said that there was no right-wing terrorism on the continent in that period.
But it added the far right was becoming very professional at producing online propaganda of an anti-Semitic and xenophobic nature and was increasingly active in online social networking.
"Although the overall threat from right-wing extremism appears to be on the wane and the numbers of right-wing extremist criminal offences are relatively low, the professionalism in their propaganda and organisation shows that right-wing extremist groups have the will to enlarge and spread their ideology and still pose a threat in EU member states," it said.
If the unrest in the Arab world, especially in North Africa, leads to a major influx of immigrants into Europe, "right-wing extremism and terrorism might gain a new lease of life by articulating more widespread public apprehension about immigration from Muslim countries into Europe", it added.
Public manifestations of right-wing extremism can often provoke counter-activity by extreme left-wing groups. Such confrontations invariably result in physical violence.
In May 2010, a far-right supporter was assaulted and knifed in Sweden during a demonstration staged by a white supremacist movement. An activist was arrested on suspicion of aggravated assault and attempted murder.
The Swedish Security Service says on its website that the so-called White Power scene is made up individuals, groups and networks with right-wing extremist views prepared to use violence for political gain.
In a speech in September 2010, Jonathan Evans, the Director-General of Britain's MI5 Security Service, cited a notorious far-right militant in a passage describing the security outlook for the country.
"Determination can take you a long way and even determined amateurs can cause devastation. The case of the neo-Nazi David Copeland, who attacked the gay and ethnic minority communities with such appalling results in 1999, is a good example of the threat posed by the determined lone bomber."
Copeland struck three targets in London with nail bombs. Three people were killed and scores were wounded at a gay bar in Soho. It followed attacks against the Muslim community in Brick Lane, east London, and a market in Brixton, south London.
In an unclassified 2011 national security outlook published by the Norway Police Security Service (PST) in February 2011, the service said it saw a picture of "increased uncertainty".
Part of that was due to what it called an expected increased level of activity in 2011 by far-right militants.
"Norwegian far-right extremists are in contact with Swedish far-right extremists, as well as with other far-right extremist groups in Europe. Contact also takes place between Norwegian and Russian far-right extremists," it said.
"An increased level of activity among some anti-Islamic groups could lead to increased polarisation and unease, especially during, and in connection with, commemorations and demonstrations."
In Britain, police chiefs and Muslim groups are worried about a rise in attacks by far-right groups, and in 2009 one senior officer, Commander Shaun Sawyer, from London's counter-terrorism unit, told a meeting of the Muslim Safety Forum that senior officers had increased surveillance of suspects to monitor their ability to stage attacks.
"I fear that they will have a spectacular ... They will carry out an attack that will lead to a loss of life or injury to a community somewhere," he said.
An analysis by Michael Whine, the Government and International Affairs Director at the Community Security Trust, an agency
of the UK Jewish community, said the willingness to employ extreme violence in defence of European 'values' is apparent in the ideology of several groups, among them the British Patriots of the White European Resistance (POWER), which emerged in 2006, and which claims supporters in Croatia, the Netherlands, Norway, Poland, Serbia, Switzerland, Slovenia, and Sweden.
Security specialist Segal said of Friday's bombing and shootings: "The tactics and actuality of these attacks would be quite striking if carried out by a domestic far-right actor - trying to kill Norway's PM is one thing and not surprising from any extremist elements, but killing average citizens in this manner is very, very unusual indeed for far-right/supremacists, and certainly for ones in Europe."