The US has intercepted two packages from Sanaa, Yemen, with explosive materials, but NBC reports that more may still remain in transit.  Investigators are looking for as many as 26 potential IEDS , both inside and outside of Yemen.  The packages discovered so far have contained the powerful explosive PETN, the same material used by the Underwear Bomber for the failed Christmas Day attack on a Northwest flight from Amsterdam:

After intercepting two mail bombs addressed to Chicago-area synagogues, investigators are searching for two dozen more suspect packages that terrorists in Yemen attempted to smuggle onto aircraft in a brazen al-Qaida terror plot.

Authorities on three continents thwarted the attacks when they seized explosives on cargo planes in the United Arab Emirates and England on Friday. …

Several U.S. officials said they were increasingly confident that al-Qaida’s Yemen branch, the group behind the failed Detroit airliner bombing last Christmas, was responsible.

A Yemeni security official said the new investigation involved about 26 suspected packages.

The bomb discovered in Dubai had a mobile phone attached to the detonator, which was wired into the printer cartridge.  The one discovered in the UK used a timer as the detonator.  That would hint at an in-air explosion as the intent rather than a target set for delivery, as that would require a specific, pinpoint prediction of actual delivery rather than just a set time when a plane would be in the air.

Clearly, though, the US believes that at least some of these are intended as attacks to specific targets inside the US.  The original tip came from Saudi intelligence, according to this report, which heard about the plot after it had apparently gone into action.  The report says that “[i]ntelligence officials were onto the suspected plot for days,” but that seems at odds with the announced timelines of the investigation, at least in the US.  The White House said yesterday that Barack Obama got informed of the plot only on late Thursday evening — and if the intel services had that much lead time, they should have been able to stop those bombs from getting on airplanes destined for the UK and Dubai.

More information will undoubtedly come out in the days ahead to shed light on some of these questions, and hopefully in the meantime investigators will track down the remaining packages before anyone gets hurt.