Sources on Twitter are reporting an explosion or explosions near the finish line of the Boston Marathon. There's not much more information as of yet. We'll update as more information comes.

More photos are coming in all the time.

12:04 pm: CBS has live video of the finish line:

12:09 pm: The AP says there were two explosions.

12:17 pm: Reuters is live-blogging with photos and tweets. Boston's Fox 25 is streaming live coverage.

12:26 pm: The Boston emergency services live audio feed can be found online right here. The police are calling for experts to investigate a suspicious truck right now.

12:39 pm: Video of the explosion can be found here.

12:57 pm: Boston Police are purposefully detonating an unexploded device near the Boston Public Library.

1:04 pm: There's a lot of untrue information floating around right now. I'm trying to sift the rumors from the truth. At the moment, this ThinkProgress post is doing as good a job as I've seen of separating the facts from speculation. The Boston PD Twitter feed says that 23 are injured and two are dead.

1:20 pm: AP says two unexploded devices have been found and are being dismantled. Boston Fire Department will be giving a press conference in ten minutes. In the meantime, here's some horrible information: The final mile of this marathon was dedicated to the victims of the Newtown shooting.

Some of the parents from the tragic school shooting in Newtown, Conn are making the two and a half hour drive up to Boston to participate in the run as their own way of honoring the victims. They are honoring the twenty children as well as the six educators who were gunned down last December. The Boston Marathon itself is honoring the 26 victims of the shooting with a special marker that is set up at the end of mile 26. The marker is the city seal and is adorned with a star for each victim.

1:51 pm: Graphic video of the first explosion has just been posted at the Boston Globe. The Globe is saying that 64 people are wounded. Here's video of the second explosion.

1:55 pm: Massachusetts Governor Deval Patrick is telling everyone to avoid crowds and go home. BPD is requesting video and eyewitness information, and Boston Police Commissioner Edward Davis just confirmed that BPD is investigating a third explosion at JFK Library for a possible connection to the Marathon explosions, although he didn't have any information about injuries from that explosion.

2:06 pm: Cell phone service in Boston is being shut down to prevent remote detonation of explosives. AP just retracted this story. Tonight's Bruins game has been cancelled.

2:16 pm: Google has launched a Person Finder for people to get information about loved ones who were expected to be in the area around the time of the explosion. The last time they did this was during the Haiti earthquake.

2:25 pm: Sean Whitcomb at SPD Blotter writes:

Our thoughts are with the people of Boston, the athletes participating in the Boston Marathon and their families.
We have been in communication with the Mayor’s Office and the Office of Emergency Management. We haven’t received any information to indicate that there is a threat to Seattle. Still, we have begun taking reasonable precautions to protect our community.
On duty resources have been directed to increase their patrols in our neighborhoods and around our infrastructure. Seattle residents may see an increased police presence.
We are also asking for public support. Please report any suspicious activity to 911.

2:36 PM: Boston PD says to ignore the New York Post's report that a suspect is in custody.

2:38 PM: Police have arrested a man on Boston Common. Eric Twardzik is live-tweeting this event, but please bear in mind that there likely could be no connection to the bombings.

2:44 pm: President Obama will speak about the bombing in twenty-five minutes.

3:04 pm: Here's a link to the White House livestream, which starts in 6 minutes.

3:10 pm: Here's President Obama. "We don't yet have all the answers, but we do know that multiple people have been wounded, some gravely." He says Homeland Security is en route and pledges "every single federal resource necessary" to support Massachusetts. "We still do not know who did this and why," President Obama says, urging us that "we should not jump to conclusions." But he promises that "any responsible individuals, any responsible groups, will feel the full weight of justice...We will find out who did this and we will hold them accountable." And then he's out, to the sounds of a gaggle of reporters asking whether it's terrorists. President Obama did not mention the word "terrorist," and now the media is chewing on that bit of information.

3:51 pm: The White House just clarified that it's handling the explosions as an "act of terror."