Tight U.S., European security measures to foil terrorists’ schemes after explosives detected aboard civilian planes

Washington: Ibrahim Asiri was the one who prepared explosive parcels

Obama: Al-Qaeda still planning terrorist attacks in America

No concerns over Suez Canal navigation

US law enforcement officials searched for suspicious packages aboard planes as President Barack Obama said that two parcels from Yemen apparently contained explosive material and were a "credible terrorist threat."

The discovery of the suspicious packages overnight on cargo planes in transit for the United States -- one in Dubai and the other in Britain's East Midlands airport -- sparked an international security alert.

Both were addressed to synagogues in Chicago.

The White House said it was tipped off by Saudi Arabia to the threat and was "grateful ... for their assistance in developing information that helped underscore the imminence of the threat emanating from Yemen."

Obama immediately ordered cargo planes at Philadelphia and Newark international airports to be towed to isolated areas and checked because they were thought to contain further packages from Yemen.

US and Canadian fighter jets were scrambled to accompany an Emirates plane into New York but Emirati authorities later said it was not carrying cargo from Yemen.

"We will continue to pursue additional protective measures as long as it takes to ensure the safety and security of our citizens," Obama told a special press conference at the White House.

Top officials reassured the public that the threat level to the United States was unchanged, although the Department of Homeland Security announced it had boosted security measures.

The president made it clear he suspected Al-Qaeda's Yemeni-based affiliate of being behind the plot, which could have serious ramifications for the global cargo industry.

"Although we are still pursuing all of the facts, we do know that the packages originated in Yemen," Obama said.

"We know that Al-Qaeda in the Arabian Peninsula, the terrorist group based in Yemen, continues to plan attacks against our homeland, our citizens, and our friends and allies."

Yemeni officials said their government had launched a full investigation and was working closely with international partners, including the United States.

"This probe is being carried out in coordination with the competent authorities in the United Arab Emirates, Britain and the United States, and its results will be announced in due time," a Yemeni government spokesman was quoted as saying last week by the state-run Saba news agency.

Obama's top counter-terrorism adviser John Brennan told reporters that it appeared "there were explosive materials in both of the packages" addressed to synagogues in Chicago.

US media reported that the packages, which held a wire-rigged ink toner cartridge and suspicious powder, may have contained the explosive PETN, the same substance used by would-be 2009 Christmas day bomber Farouk Abdulmutallab and 2001 attempted shoe-bomber Richard Reid.

In Dubai, a police statement said the parcel intercepted there bore Al-Qaeda hallmarks including a powerful explosive and mobile phone detonator concealed in a computer printer.

It said the bomb was a complex and professional device made of PETN and lead -- a highly explosive combination that can cause great damage.

British authorities were probing whether the package contained a "viable" bomb, Home Secretary Theresa May said.

In the hours following the discovery of the packages, the US authorities gave advance warning to Jewish leaders in Chicago of a threat against synagogues in the city.

However, synagogues in Chicago planned to hold regular services.

"It’s obviously disturbing," Rabbi Michael Balinsky, executive vice president of the Chicago Board of Rabbis, told The New York Times. "But certainly the Jewish community will proceed as it proceeds. We’ll just exercise caution."

The cargo scare offered a new twist as Western authorities have usually focused on dangers posed to passenger airliners following the September 11, 2001 attacks, when Al-Qaeda hijacked planes and struck targets in New York and Washington.

Yemen, the ancestral homeland of Al-Qaeda leader Osama bin Laden, faces a growing threat from the local branch of his global jihadist network.

Over the past decade, it has become a haven for violent extremists, becoming the headquarters of Al-Qaeda in the Arabian Peninsula and the hiding place for US-born radical cleric Anwar al-Awlaki, who has been linked to high-profile terror plots in the United States.

Oren Segal, director of the Anti-Defamation League's Center on Extremism in Washington, said that if Al-Qaeda in the Arabian Peninsula is behind the plot, it may have chosen Chicago as a target because it is the hometown of the US president.

"They may be trying to send a message to Obama that they can attack his backyard as well," said Segal.

Ibrahim Hassan al-Asiri, a prominent member in al-Qaeda's Yemen Branch, suspect in 2009 Christmas plot, is suspected anew.

He is suspected of packing explosives into the underwear of a Nigerian accused of trying to blow up a Detroit-bound airliner last Christmas and sent his own brother on a suicide mission against a top Saudi official.

Ibrahim Hassan al-Asiri, considered a key figure in al Qaeda's most active franchise, is now the chief suspect behind the mail bombs sent from Yemen and bound for the United States, according to U.S. intelligence officials.

Together with a U.S.-born preacher, Yemeni militants, and former Saudi inmates of Guantanamo, al-Asiri makes up the leadership of Al Qaeda in the Arabian Peninsula (AQAP).

CBS News homeland security correspondent Bob Orr reports that U.S. officials now have no doubt the Yemen-based al Qaeda franchise was behind the cargo bomb plot.

Sources tell CBS News that about 15 other "suspect" packages sent from Yemen around the same time as the bombs have now been located and cleared. But, Orr reports, officials have voiced concern that there could be more explosive packages out there.

An official security source said that United Arab Emirates authorities are tracing the serial numbers of a mobile phone circuit board and computer printer used in the mail bomb sent from Yemen and found in Dubai.

The source told The Associated Press the UAE is sharing the numbers with other countries including the United States in an effort to track the origins of the bomb parts. The person spoke on condition of anonymity because the investigation is ongoing.

Whatever the outcome of the investigation, sources say AQAP presents a long term threat to the U.S.

Forensic analysis indicates that al-Asiri, who is living in Yemen, built all three devices and is believed to have a fair degree of skill and training, although all the operations have been unsuccessful.

British Home Secretary Theresa May said the bomb discovered on the plane that landed in England was powerful enough to bring down the aircraft. A U.S. official and a British security consultant said the device, hidden in a printer cartridge, was sophisticated enough that it nearly slipped past British investigators even after they were tipped off.

Yemeni security officials said they are searching for al-Asiri, who is believed to be in Marib province.

His most effective operation was the attack on top Saudi counterterrorism official Prince Mohammed bin Nayef, in which he recruited his younger brother, Abdullah, to pose as a repentant militant.

CBS News reported that Abdullah al-Asiri managed to get through two airport security screenings by hiding about a pound of explosives and a detonator in his rectum. The prince was only wounded, but al-Asiri's body was blown apart by the blast.

Meanwhile, Egypt has tightened security along the Suez Canal following the bombing of a U.S. destroyer in Yemen earlier this month, an official on the Suez Canal Board said.

The official told United Press International "security measures in the international maritime canal were consolidated after the attack on the USS Cole destroyer in Aden three weeks ago and which resulted in U.S. warships to refrain from using the canal to and from its bases in the Gulf region."

He said "despite the safety of the ordinary security measures in the Suez canal, other precautionary measures were adopted with the aim of assuring the U.S.