Authorities in Britain and Dubai seized two explosive packages addressed to Chicago area synagogues on cargo jets. They said the packages originated from Yemen carried by Fedex and UPS parcel services.
In a statement distributed to journalists and appearing on the official website, the government said there were no UPS cargo planes that had taken off from Yemen or any indirect or direct flights to British or American airports.
The statement warned against "rush decisions in a case as sensitive as this one and before investigations reveal the truth."
The government also promised an investigation into allegations that the packages had originated in Yemen.
The discovery of the packages has once more put the spotlight on the violence-wracked, poverty-stricken country on the Arabian Peninsula.
If the explosive devices shipped in cargo planes from Yemen are conclusively linked by investigators to the al Qaeda faction in Yemen, it could represent a new tactic by al Qaeda in the Arab Peninsula.
The group previously has spawned plots against commercial U.S-bound flights and had a role in mass shootings in several American cities.
In the past 18 months, the al Qaeda offshoot in Yemen has grown stronger, and its members have been implicated in several plots against U.S. targets, including the futile attack last Dec. 25 on an airliner landing in Detroit, Michigan.
Next to Osama bin Laden and his al Qaeda leaders in Pakistan, al Qaeda in the Arabian Peninsula is considered the most active al Qaeda threat to the United States and its Western allies, according to the Obama administration.
"What you have is a hardened core of al Qaeda operatives operating in the safe haven of Yemen trying to hit the United States and trying to do it creatively and effectively," said CBS News senior national security analyst Juan Zarate.
It's not yet clear that the devices contained enough material - or the right combination of materials to produce an explosion, reports CBS News justice correspondent Bob Orr. But al Qaeda in the Arabian Peninsula has experienced bomb makers. Previous explosives have been hidden in cassette cases, picture frames and radios. Officials do not know if the devices were designed to explode in the air or needed to be detonated by a person on ground, presumably once they arrived in Chicago.
The United States has reinforced its military and intelligence assistance to Yemen, including the potential addition of armed Predator drones to be operated by the CIA. The Pentagon is sending more than $150 million in military aid, including helicopters, planes and other equipment.
There have been a number of airstrikes into Yemen that have taken out insurgent leaders, with either coordination from the United States or direct involvement, but officials will not talk about them.
AQAP includes as many as 300 members or cells operating out of Yemen. A top leader is Anwar al-Awlaki, the American-born radical cleric who is believed to have helped plan the Dec. 25 attack and inspired other attacks, including the shooting massacre at Fort Hood, Texas, last year. He is on a U.S. government secret list of targets to be captured or killed.
During the past year, the number of elite U.S. trainers moving in and out of Yemen has doubled, from 25 to about 50 now. And the U.S. forces are providing more complex instruction that combines tactical ground and air operations.
Yemen is the poorest Arab country, with 45.2 percent living below the poverty line, according to the CIA factbook.