Very early reports of an explosion within the U.S. embassy compound in Athens...

UPDATE: CNN International is giving two contradictory pieces of information - one is that "chaos" is going on within the compound, the other is that the Embassy is reporting no injuries.

This is pure speculation, but — gas leak? It would be, what 7 a.m. out there? If this happened within the hour, between 6 and 7 a.m. local time?

The fact that this explosion is reported within the compound makes it more ominous if it is, ultimately, terrorism; on the other hand, past terror attacks on embassies have all involved somebody on the outside trying to hurt people within.

The next thought - very ominous from where I'm sitting, half asleep - is that if this is al-Qaeda, they may use their style of multiple simultaneous attacks...

The AP has a brief item up...

UPDATE: It must be either not that bad, or very hard to get information about this in Athens, because CNN International is telling me about David Beckham going to the Los Angeles Galaxy...

Athens media sources are reporting the explosion was "of significant size," whatever that means...

Anthee Carassavas is in Athens, telling CNN  "officials leaning hypothesis of terrorist atack", officials are speculating that a rocket-propelled grenade launched from outside the compound. Explosion was near the Ambassador's office; the Ambassador is currently safe and secure. (I'll bet very few employees were at work at that hour.)

UPDATE: Several hours later, we are informed it was an anti-tank shell:

An anti-tank shell was fired at the U.S. embassy early Friday, striking the front of the building but causing no injuries. Greece's Public Order Minister said the blast was probably an act of domestic terrorism - raising fears of resurgent violence by far-left Greek militants.

While it's reassuring that this wasn't al-Qaeda, and that there were no casualties, I've wondered if or when we would see other terror groups imitating al-Qaeda's mass-casualty "superterrorism" methods. Had they done this later in the day, the results could have been much worse.

For example, in Spain, ETA blew up a parking garage at the Madrid Airport a few weeks ago. The bomb only killed two people, but the devastation reminded me of Oklahoma City - clearly, it could have been much worse.

ETA is also claiming, by the way, that despite the fact that they blew up a parking garage and killed two people, the "ceasefire" is still in effect.

Hey, guys, let's go over the definition of "ceasefire" again.