A frantic international search for suspicious packages netted two potentially deadly explosive devices bound for Chicago synagogues - and prompted terror scares in Brooklyn and at area airports.
President Obama deemed the packages a "credible terrorist threat against our country" and vowed the enemies of the United States would not prevail.
"Counterterrorism professionals are taking this threat very seriously and are taking all necessary and prudent steps to ensure our security," Obama said in a hastily called press conference Friday, just days before the midterm elections.
The devices - one found in the United Kingdom, the other in Dubai - originated in Yemen, a hotbed for terror groups, including a dangerous Al Qaeda offshoot, officials said.
Preliminary tests showed the devices contained PETN, the powdered chemical used by Umar Farouk Abdulmutallab, the failed Christmas Day underwear bomber. Abdulmutallab, who was flying from Amsterdam to Detroit, trained in Yemen.
The scare prompted authorities to evacuate several downtown Brooklyn office buildings, search cargo planes in Philadelphia and Newark and dispatch fighter jets to escort a flight from the United Arab Emirates to Kennedy Airport.
Two packages inside a UPS truck at MetroTech - later found to be envelopes from Yemen - temporarily shut down the Manhattan Bridge and part of Flatbush Ave.
The items in Brooklyn were cleared after an NYPD X-ray of the envelopes revealed they simply contained bank receipts and other papers.
Federal officials were cautiously optimistic the plot was thwarted, but they warned the threat was real.
"A traditional dry run would not use explosive materials," said John Brennan, deputy National Security Adviser for Homeland Security and Counterterrorism.
The White House thanked the Saudis for providing key intelligence, including tracking numbers for the packages.
President Obama learned Thursday night of the initial threat in the UK.
"We know that Al Qaeda in the Arabian Peninsula, the terrorist group based in Yemen, continues to target our homeland, our citizens and our friends and allies," Obama said.
The Anti-Defamation League warned Jewish institutions across the country to bolster security, particularly in Chicago. The synagogue across from Obama's Hyde Park house was not one of the houses of worship targeted, officials said.
Intelligence personnel had been monitoring a suspected plot for days after the Saudi tip, officials said. Law enforcement first mobilized after a suspicious package from Yemen was found in a UPS facility outside London.