Here's the embassy alert.
This Warden Message is to inform U.S. citizens residing and traveling in Guatemala that the U.S. Embassy has learned of a potential threat to Embassy facilities. As a precaution, our security office has put in place additional security measures. The Embassy is open for business as usual, but there may be traffic disruptions related to the new security measures.
The Department of State remains concerned about the continued threat of terrorist attacks, demonstrations, and other violent actions against U.S. citizens and interests overseas...The Department of State issued this Worldwide Caution to update information on the continuing threat of terrorist actions and violence against U.S. citizens and interests throughout the world. U.S. citizens are reminded to maintain a high level of vigilance and to take appropriate steps to increase their security awareness.There's nothing specific in the warning but it does seem more than your run of the mill warning. From the warning, it is the Embassy itself that is the target and not any person in particular.
The list of recent crimes against Americans in Guatemala that have been reported is pretty unnerving, but then again Guatemala's not the safest place in the hemisphere. (I hadn't read this before, but there was a US citizen on the bus that exploded back in early January when several people died. The resident escaped through the window after the explosion).