WASHINGTON (AP) -- Authorities on three continents thwarted multiple terrorist attacks aimed at the United States Friday, seizing two explosive packages addressed to Chicago-area synagogues and packed aboard cargo jets from Yemen. Parts of the plot might remain undetected, President Barack Obama's counterterror chief warned.
Obama called the coordinated attacks a "credible terrorist threat" amid worldwide fears that al-Qaida was launching a major new campaign of assaults.
"The United States is not assuming that the attacks were disrupted and is remaining vigilant," Obama adviser John Brennan said at the White House.
One of the packages was found aboard a cargo plane in Dubai, the other in England. In the U.S., cargo planes were searched up and down the Eastern Seaboard, and an Emirates Airlines passenger jet was escorted down the coast to New York by American fighter jets.
No explosives were found aboard those planes, though the investigation was continuing on at least two.
Obama's sobering assessment, delivered from the White House podium, unfolded four days before national elections in which discussion of terrorism has played almost no role. The president went ahead with weekend campaign appearances.
The terrorist efforts "underscore the necessity of remaining vigilant against terrorism," the president said. While he said both packages that contained explosives originated in Yemen, he did not explicitly assign blame to al-Qaida, which is active in the Arab nation and long has made clear its goal of launching new attacks on the United States.
Authorities in Dubai intercepted one explosive device. The second package was aboard a plane searched in East Midlands, north of London, and officials said it contained a printer toner cartridge with wires and powder. Brennan said the devices were in packages about the size of a breadbox.
While the president didn't specifically accuse Yemen's al-Qaida branch, officials who spoke on condition of anonymity said they were increasingly certain that was the source. The same group was responsible for the attempted bombing of a U.S.-bound airliner last Christmas.
The radical U.S.-born Muslim cleric Anwar al-Awlaki, who now lives in hiding in Yemen, is believed to have helped inspire recent attacks including the Fort Hood shooting, the Times Square bombing attempt and the failed Detroit airliner bombing last Christmas Day.
Most of the officials spoke on condition of anonymity, citing the ongoing investigation.
Brennan later told reporters that the explosives "were in a form that was designed to try to carry out some type of attack," but he provided no further details.
"The forensic analysis is under way," he said, adding, "Clearly from the initial observation, the initial analysis that was done, the materials that were found in the device that was uncovered was intended to do harm."
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