Al-Qaeda had bomb-plot dry run: U.S.
American officials believe al-Qaeda sent mail from Yemen to Chicago in September in a practice run for its failed bomb plot.
The three packages contained papers, books and other materials headed for Chicago, but no explosives.
Before the packages reached their destinations, U.S. authorities seized and searched the boxes. They now appear to have been sent by the Yemeni militant group al-Qaeda in the Arabian Peninsula to test the logistics of the air cargo system, a U.S. official said.
"We received information several weeks ago that potentially connected these packages to AQAP," said an official who was familiar with details of the shipments.
Last week's discovery of explosive material on flights bound for the United States had repercussions on air travel and cargo in multiple countries, including in Canada, where the government has banned all air cargo originating from Yemen.
The American official also disclosed that both mail bombs, one recovered in Dubai and the other in Britain on Friday, were wired to detonators that used cellphone technology. It still was not clear whether those detonators would have been set off by telephone calls or by an internal alarm.
The apparent dry run was first disclosed Monday night by ABC News.
The official said authorities, already aware of the militants' interest in striking at aviation, "obviously took notice" this past weekend and considered the likelihood that the militants might have extended their threat to the cargo system.
"When we learned of last week's serious threat, we recalled the [September] incident and factored it in to our government's very prompt response," the official said.
The threat last week came in the form of explosive devices hidden in the toner cartridges of computer printers. Investigators have centred on the Yemeni al-Qaeda faction's top bomb maker, who had previously designed a bomb that failed to go off on a crowded U.S.-bound passenger jetliner last Christmas.
More explosives than attempted holiday attack
This time, authorities believe alleged master bomb-maker Ibrahim al-Asiri packed four times as much explosives into the bombs hidden last week on flights from Yemen. The two bombs contained 300 and 400 grams of the industrial explosive PETN, according to a German security official.
By comparison, the bomb stuffed into a terror suspect's underwear on the Detroit-bound plane last Christmas contained about 80 grams.
"It shows that they are trying to again make different types of adaptations based on what we have put in place," said John Brennan, U.S. President Barack Obama's counterterrorism adviser. "So the underwear bomber, as well as these packages, are showing sort of new techniques on their part. They are very innovative and creative."
The U.S. and its allies Monday further tightened scrutiny of shipments from Yemen. U.S. counterterrorism officials warned police and emergency personnel to be on the watch for mail with characteristics that could mean dangerous substances are hidden inside.
Germany's aviation authority extended its ban on air cargo from Yemen to include passenger flights. Britain banned the import of larger printer cartridges by air on Monday as it also announced broader measures to halt air cargo from Yemen and Somalia.
A Yemeni government statement Tuesday expressed "sorrow and astonishment" at Germany's decision and said it was a "rushed and exaggerated reaction."
Unknown how bombs would have worked
U.S. and British officials said they believed the targets were planes, not the two Chicago-area synagogues named on the addresses.
Exactly how the bombs would have worked, however, remains a focus of investigators.
Activating a bomb by cellphone while a plane is in midair is unreliable because cell service is spotty or non-existent at high altitudes. Further complicating the plot, it be would unlikely for terrorists in Yemen to know which planes the bombs had been loaded onto and when they were airborne.
With U.S.-bound cargo out of Yemen temporarily frozen, Transportation Security Administration chief John Pistole said Monday the U.S. would provide Yemen with new screening equipment for cargo. Yemen has promised to step up its security at airports.
Nobody, including the internet-savvy al-Qaeda group in Yemen, has taken credit for the failed attack. Jihadist websites contained numerous messages praising the attempted bombing, but nothing official from the group's leadership.
Though al-Qaeda's core is based in the lawless tribal regions of Pakistan, offshoots have sprung up in other countries, including Yemen and Algeria. The Yemen group is the most active affiliate and has become a leader in recruiting and propaganda, especially in the West thanks to its English-speaking, U.S.-born spokesman, Anwar al-Awlaki.
On Tuesday, Yemeni prosecutors charged al-Awlaki in absentia with plotting to kill foreigners.
The U.S. is providing some $300 million in military, humanitarian and development aid to Yemen this year, according to State Department counterterrorism co-ordinator Daniel Benjamin.