Norway came under attack with a massive bombing in the heart of its power center and a shooting at a youth camp. Police say the attacks are linked, but no one has claimed responsibility so far.
The attacks are the largest in Europe in six years. What's behind it all? CNN's Tim Lister explains the possibility of terrorism, the potential reasons why Norway may have been a target and who may have been behind it.
CNN: What does this look like to you in terms of the sophistication of these explosions?
LISTER: It's a sophisticated effort. There's no doubt about it. In fact, this is the largest explosion of this sort since 2005, London, the subway bombings. And before that, it was Madrid.
So, six years has really been fairly peaceful in Europe. There have been plots that have been uncovered, some of them quite dangerous plots. But this is the first time that we've seen devastation of this magnitude on the streets of Europe.
And it looks like a scene out of Baghdad or Beirut. It's a massive blast that must have been planned well ahead of time. This is not a lone wolf operation.
CNN: So, if it's sophisticated, does that mean it could be terrorism?
LISTER: I think the betting is on terrorism. We don't know for sure, yet. But you've only got to look at the sort of blast that occurred. You've only got to look at the target - prime minister's office, the headquarters of the major newspaper group next door.
Why would that be relevant? Because the Norwegian newspapers republished the cartoons of Prophet Mohammad that caused such offense in the Muslim world. When that happened, the Norwegian telecoms offices in Pakistan were attacked and ransacked. The Norwegian embassy in Damascus was attacked. That is an issue that still rankles amongst Islamist militants the world over.
So, that fact that Norwegian newspapers did that makes them a target.
CNN: How much damage do you think these bombs were capable of doing? What's your best guess on that? We're not even sure where they were if they were car bombs or where they were.
LISTER: We're not sure. I was speaking to a Norwegian close to the scene of the blast. And he wasn't sure if it came from inside or outside the building. But he said the shock wave was immense. And that suggests it was a high amount of commercial explosives involved because the shock wave, if it traveled to where he was, would have to have been detonated by a really substantial bomber.
CNN: And why do you think Norway?
LISTER: Norway, for several reasons. One I mentioned the cartoons.
You would have thought Norway, a small country at the top of the world, 5 million people, why? Well, they've been active in Afghanistan. They had a deployment there for several years. They're active in the Libyan air campaign, the cartoon issue.
But also, what we're finding in Scandinavia is that groups themselves are coming together from Denmark, Sweden, and Norway, different ethnicities, very often gathering and meeting in mosques, and they're local to Norway, Sweden, Denmark. They know where the targets are.
And just last week, there was a man who lived in Norway, who's head of Ansar al-Islam, a very radical Sunni group from northern Iraq, who was prosecuted because he'd threatened Norwegian ministers because he was going to be deported. He said, you deport me and I get killed in Iraq, the same will happen to Norwegian ministers.
So, they do have this fringe in Scandinavian countries of Islamist militants. And they're only just getting grips with that.
CNN: In terms of who might be behind this, who do you think?
LISTER: It could be a whole range of groups. But the point is that al Qaeda is not so much an organization now. It's more a spirit for these people. It's a mobilizing factor.
When they're gathering in cells, they don't necessarily have big structures that are transnational. But what we are seeing is that some of these people, especially in Scandinavia over the last five years, have gone to Somalia. They've gone to Pakistan. They've gone to Afghanistan. They linked up with various jihadist groups, some of them have been trained in bomb making, and sabotaging, assassinations, and they've come back.
And if there's one thing that worries authorities across Europe now, from Germany, United Kingdom, Scandinavia, it's those people who are residents of Europe, who have gone overseas and have come back - trained and ready to give their lives or to sow mayhem.
CNN: How will they go about trying to find out who did this? How will they piece the evidence together? What will they be looking for right now on the scene?
LISTER: One thing we know is that the intelligence agencies in Norway and Sweden and Denmark have been on the highest state of alert for the last nine months. They've been looking at these terrorist chatter. Now, they're going to pour much more resources into that - who's involved, which mosques may have been basis for militancy, for example.
But in the immediate hours, they will want to find as much forensic evidence from the bomb, its packaging, maybe a vehicle identification number, CCTV from the area, all of that will come into place straight away. The most important thing they get is the signature of the bomb or what was - what it was in, what was carrying it, was it a vehicle? Was it dumped in a garbage can, for example, and left there.