Suspicious packages from Yemen intercepted in Dubai and England tested positive for explosives, according to President Obama, addressing the nation Friday afternoon about what he now calls "a credible terrorist threat against our country."

"Last night and earlier today," said President Obama, "intelligence and law enforcement officials working with our friend and allies identified two suspicious packages bound for the United States, specifically two places of Jewish worship in Chicago."

"Initial examination of those packages determined that they do apparently contain explosive material."

The president said the packages had come from Yemen, and that he had "directed that we spare no effort in investigating the origins of these suspicious packages and their connection to any additional terrorist plotting."

The president vowed to enhance screening of cargo planes in the U.S., and said he had been in touch with the president of Yemen.

For the Chilean miners who have been trapped half a mile under the ground for the last two months, there is literally light at the end of the tunnel.

On Saturday a rescue drill reached the underground chamber where the 33 miners have been entombed since August 5. A siren rang at "Camp Hope," the tent camp outside the mine, signifying the drill's breakthrough, which prompted celebration of the families who had been holding vigil, according to The Associated Press.

The so-called Plan B Schramm T-130 drill carved a hole wide enough for an escape capsule to pull the miners out; the men could be hoisted to freedom as early as Tuesday.

Watch "World News with Diane Sawyer" for more on this story tonight on ABC.