WASHINGTON (AP) -- Authorities on three continents are investigating whether suspicious packages shipped from Yemen to Chicago religious sites are part of a terrorist plot.
Officials were investigating whether two packages -- one described as containing a toner cartridge with wires attached and powder -- were mailed as part of an attempted attack or a dry run for a future attack.
No explosives have been found in the U.S. Packages in England and Dubai continue to be tested.
Yemen is home to the al-Qaida branch that tried to bomb a Detroit-bound airliner on Christmas.
The packages were discovered in England and Dubai late Thursday after a foreign intelligence service picked up information related to Yemen and passed it on to the U.S., one official said.
U.S. national security officials alerted President Barack Obama to a "potential terrorist threat" after they were found, the White House said. Obama planned a public statement on the developments later Friday.
The two packages were addressed to Chicago religious sites, Chicago FBI spokesman Ross Rice said. Both were sent from the same address in Yemen, and one of the packages was addressed to a synagogue, said a U.S. official who spoke on condition of anonymity to discuss the ongoing investigation.
The package in England, discovered aboard a plane in East Midlands about two hours north of London, contained a toner cartridge with wires and powder. It was found during routine screening of cargo in England, prompting authorities to scour three planes and a truck in the United States on Friday, U.S. officials said.
"The president directed U.S. intelligence and law enforcement agencies, and the Department of Homeland Security, to take steps to ensure the safety and security of the American people, and to determine whether these threats are a part of any additional terrorist plotting," the White House said in a statement.
Yemeni officials said they launched a terrorism investigation and Scotland Yard said its investigators were testing a number of items seized from the plane in East Midlands.
In the U.S., searches were conducted in Philadelphia, Newark, N.J., and New York City. Local officials said all of the suspicious items and planes that were searched have been given the "all clear."
"As a precaution, DHS has taken a number of steps to enhance security," the Homeland Security Department said in a statement. "Some of these security measures will be visible while others will not."
Since the failed Christmas bombing of a Detroit-bound airliner, Yemen has been a focus for U.S. counterterrorism officials. Before that attack, the U.S. regarded al-Qaida's branch in Yemen as primarily a threat in the region, not to the United States.
The Yemen branch known as al-Qaida in the Arabian Peninsula has since become a leading source of terrorist propaganda and recruiting. Authorities believe about 300 al-Qaida members or cells operate in Yemen.
The Yemeni government has stepped up counterterrorism operations, with help from the U.S. military and intelligence officials. Mohammed Shayba, general-director of the state airline's cargo department, said the government is conducting an investigation.
"Those in charge are in constant meetings and they are investigating and taking the issue seriously," he told The Associated Press.
Sarah Furbank, a passenger who was about to board a plane out of East Midlands Airport, said she had noticed an increased security presence.
There were "quite a few police cars round the edge" of the airport, Furbank told The Associated Press. "Apparently there was an incident earlier according to staff but they didn't go into detail."