Security forces in Yemen arrested a female suspect Saturday, who the country's President says shipped two bombs hidden in printers to synagogues in Chicago.
Yemen President Ali Abdullah Saleh made the announcement in Sanaa, the country's capitol, according to reports from Reuters.
A spokesman at the Yemeni embassy in Washington, D.C. said he could not confirm the arrest.
President Saleh said the woman was taken into custody after Yemeni security forces surrounded a home at an undisclosed location earlier in the day.
The packages were both shipped earlier in the week, one by FedEx and the other by UPS, both destined for Chicago.
The Saudi Arabia intelligence service provided extensive information about the plot including the FedEx and UPS tracking numbers, according to Homeland Security Secretary Janet Napolitano.
"We were able to identify them by where they were emanating from and package number, where they were located," Napolitano said this morning on the ABC News program Good Morning America.
In Chicago, the Or Chadash synagogue whose members are primarily gay and lesbian Jews said it had been notified it was one of the two targets of the terror plot.
Or Chadash shares space with another synagogue, the Emanuel Congregation.
The communications director of Emanuel Congregation told ABC News today that she noticed an unusually high number of hits on the temple's website from an IP address in Cairo a few weeks ago, but didn't think anything of it until now.
Elsewhere Saturday, US officials continued to check out other packages sent to the United State from Yemen, but said they believed they had contained the immediate plot.
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 called "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 initial intelligence report from Saudi intelligence said there could be as many as 15 bomb packages being sent from Yemen to the U.S. None have yet been discovered in the U.S.
The initial report came late Thursday night and involved two separate packages shipped from Sanaa, Yemen to Chicago, according to law enforcement officials. The package intercepted in Dubai was shipped via FedEx, the one stopped in the U.K. by UPS.
Officials said both packages were stopped midway on their trip to Chicago, one at the East Midlands cargo airfield outside London and the other at the airport in Dubai.
US officials told ABC News that the package stopped in Dubai contained cell phones and what might be "detonators and timers." Officials said the second package, intercepted in the U.K., contained a printer whose toner cartridge appeared to have been tampered with and contained white powder -- nearly a pound of it -- instead of black powder, arousing suspicion.
According to sources, the devices were constructed by gutting a toner cartridge and installing a complete improvised explosive inside it -- a detonator, main charge and cell phone initiator. One source gave an initial estimate that 10 to 14 ounces of homemade high explosive were contained in the devices.
Officials believe that the powder may be the explosive PETN, used in the failed plots of the so-called shoe bomber and underwear bomber.
White House spokesman Robert Gibbs said that as a result of the discovery of the packages, "additional measures were taken regarding . . . flights at Newark Liberty and Philadelphia International Airports."
The discovery of the packages led to an international search of cargo planes carrying packages to the United States from Yemen today.
Authorities in Newark and Philadelphia searched UPS and FedEx cargo jets. US fighter jets also escorted Emirates Air flight 201 from Dubai into John F. Kennedy airport in New York City this afternoon. According to a statement from NORAD, the plane was determined to be "an aircraft of interest."
Gibbs said President Obama was notified of a potential terrorist threat Thursday night by John Brennan, deputy national security advisor for counterterrorism, at 10:35 p.m. "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 president vowed to enhance screening of cargo planes in the U.S., and said he had been in touch with the president of Yemen.
Brennan issued a statement thanking Saudi Arabia "for their assistance in developing information that helkped underscore the imminence of the threat emanating from Yemen." Brennan also thanked the U.K. and the United Arab Emirates for their assistance.
There had been conflicting reports about whether either of the two intercepted packages tested positive for explosives. British and US officials initially reported that tests for explosives were negative, but other American law enforcement officials said at least one, possibly both, contained explosives. In a statement late Friday, British officials said only the "suspect package" was "currently being examined."
The package being examined in the UK also included a portion of a cellphone.
British Home Secretary Theresa May said that "a suspect package was discovered during a search of a cargo flight at East Midlands airport." May said the package originated in Yemen and was addressed to a destination in the US.
A FedEx official confirmed that a suspicious package shipped from Yemen had been "confiscated" at the FedEx facility in Dubai. Local authorities confiscated the package in cooperation with the FBI.
In a statement, the Department of Homeland Security said it was taking steps to enhance air security. "Some of these security measures will be visible while others will not," said the statement.
"The public may recognize specific enhancements including heightened cargo screening and additional security at airports. Passengers should continue to expect an unpredictable mix of security layers that include explosives trace detection, advanced imaging technology, canine teams and pat downs, among others. As always, we remind the public to remain vigilant and report suspicious activity to local law enforcement."
A spokeswoman for the Jewish Federation of Chicago told ABC News the federation was alerted this morning and passed on the alert, advising local synagogues to take security precautions. She also said the group was not one of the targets.
The FBI's Chicago office said that the packages "in question" had been addressed to two Chicago locations, but would not provide further details. The FBI "notified the targeted institutions" by phone this morning, according to a spokesman. The White House said that the synagogue across the street from the president's home in Chicago was not one of the synagogues targeted.
The Anti-Defamation League released a statement that said it had learned from "law enforcement sources" of a reported threat to Jewish institutions in packages shipped from the U.K., Yemen and Saudi Arabia, and that it had sent notice to Jewish organizations across the U.S.
While President Obama did not say that Al Qaeda in the Arabian Peninsula was behind the apparent bombing attempt, he did note in his afternoon address that Al Qaeda's Yemeni offshoot continues to seek ways to attack the United States.
The radical American-born cleric Anwar a-Awlaki has repeatedly called on for attacks on the U.S. from his base in Yemen.
American officials believe that AQAP has trained hundreds of terrorists whose prime objective is to attack the US, including the so-called underwear bomber Umar Farouk Abdulmutallab.
"Yemen is the home of between 500 and 600 al Qaeda fighters, three or four times the number of al Qaeda fighters in Afghanistan," said Richard Clarke, former White House counterterrorism official and now an ABC News consultant. "This is really a place where Al Qaeda is operating, where it's strong, where it has training camps, where we know they have trained people and sent them to the United States."
U.S. authorities have now ordered every package shipped from Yemen to the U.S. to be inspected.
FedEx also said in a statement that local authorities, in cooperation with the FBI, had "confiscated a suspicious package at the FedEx facility in Dubai. The shipment originated in Yemen and as an additional safety measure, FedEx has embargoed all shipments originating from Yemen."
The method of trying to ship the improvised explosives into the country on air cargo flights exposed one of the worst-kept secrets about American security.
At best, only a third of packages coming into the country as air cargo are ever inspected.
"I've called cargo the soft underbelly of aviation security because of the relative little security that is attached to it," said Clark Kent Ervin, former inspector general of the Department of Homeland Security. "I think this just underscores that fact that al Qaeda is always probing for weaknesses in the system and when we close one vulnerability, al Qaeda is just going to find another."
Tonight, Homeland Security agents and intelligence analysts were ordered to go back through previous shipments from Yemen over the last two weeks, as the White House worried that other package bombs might have already made their way into the country.
RICHARD ESPOSITO, PIERRE THOMAS, JACK CLOHERTY and JIM SCIUTTO contributed to this report.