Obama: Incident a “Credible Terrorist Threat”

President Barack Obama declared Friday that authorities had uncovered a "credible terrorist threat" against the United States following the overseas discovery of U.S.-bound packages containing explosives aboard cargo jets.

Obama said both had been addressed to Jewish organizations in the Chicago area. The events "underscore the necessity of remaining vigilant against terrorism," the president said.

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

One of the packages was found aboard a cargo plane in Dubai, the other in England. Preliminary tests indicated the packages contained the powerful industrial explosive PETN, the same chemical used in the Christmas attack, U.S. officials said. The tests had not been confirmed.

The packages were addressed to a Jewish community center and synagogue in the area, but the exact locations weren't released.

Earlier reports indicated that Temple Sholom synagogue on the North Side was one of the targeted locations, but Rabbi Aaron M. Petuchowski told NBC Chicago that his place of worship was not a target.

"There is a sense of concerned, and justified concern, and our prayers are offered on behalf of all of those throughout God's world who feel, or are in fact a target of terrorist activities," Petuchowski said.

Chicagoans of Jewish faith remained unfazed by the planned attack.

"I'm Jewish, I'm not afraid and we keep on going," Sandy Kurtz said as she left Sabbath services. "We've survived for thousands of years and will continue. Very strong people."

But despite that confidence, Jewish leaders across the city are tweaking their security systems and testing their emergency response plans.

Across 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 plans to go ahead with weekend campaign appearances, including a rally in Chicago Saturday night.