PARIS — American and British officials moved quickly Thursday to downplay the French foreign minister's comment that one of two mail bombs sent from Yemen last week was disarmed just 17 minutes before it was set to go off.
The issue of timing is central to the investigation because it could indicate whether terrorists hoped to blow up the planes over U.S. airspace or whether they simply wanted to take down the planes regardless of their location.
"One of the packages was defused only 17 minutes before the moment that it was set to explode," French Interior Minister Brice Hortefeux told state-run France-2 television. He made no other comment on the Yemen mail bomb plot in the interview and was not available afterward.
One law enforcement official told NBC News on Thursday that the U.S. cannot confirm the 17-minute timer claim by the French minister.
White House press secretary Robert Gibbs said the question of when the bombs found in Britain and the United Arab Emirates were to go off was still under investigation and there was no information confirming such a close call.
U.S. State Department counterterror coordinator Daniel Benjamin also questioned the French minister's comments.
"This is not our understanding of the situation. Our understanding is the investigators are still looking at the fusing and the timing of a possible detonation so I can't confirm that right now," he told reporters in Rotterdam.
A government official in Britain said the device found there was still undergoing forensic tests and it had not been determined how close it was to being detonated. A security source in the United Arab Emirates said Hortefeux's remark did not describe the bomb found in that country.
"If this was a reference to the device found in the Federal Express (Fedex) site in Dubai, then it is not correct," a security source in the United Arab Emirates who is familiar with the investigation told The Associated Press.
Both were not authorized to discuss the case publicly and spoke on condition of anonymity.
Hortefeux did not say where he got the information about the timing, although U.S. and European intelligence officials have been exchanging information on the plot. The French Interior Ministry would not elaborate on Hortefeux's comment.
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When investigators pulled the Chicago-bound packages off cargo planes in England and the United Arab Emirates Friday, they found the bombs wired to cell phones and hidden in the toner cartridges of computer printers.
The communication cards had been removed and the phones could not receive calls, officials said, making it likely the terrorists intended the alarm or timer functions to detonate the bombs, U.S. officials have said.
They also said that each bomb was attached to a syringe containing lead azide, a chemical initiator that would have detonated PETN explosives packed into each printer cartridge.
Both PETN and a syringe were used in the failed bombing last Christmas of a Detroit-bound airliner.
Investigators have centered on the Yemeni al-Qaida 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.Video: Dry run may have preceded al-Qaida bomb plot (on this page)
This time, authorities believe that 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, who briefed reporters Monday in Berlin on condition of anonymity in line with department guidelines.
By comparison, the bomb stuffed into a terrorist suspect's underwear on the Detroit-bound plane last Christmas contained about 80 grams.
One of the explosive devices found inside a shipped printer cartridge in Dubai had flown on two airlines before it was seized, first on a Qatar Airways Airbus A320 jet to Doha and then on an as-yet-undisclosed flight from Doha to Dubai.
The number of passengers on the flights were unknown, but the first flight had a 144-seat capacity and the second would have moved on one of a variety of planes with seating capacities ranging from 144 to 335.
The packages were addressed to two Chicago-area synagogues. Because the addresses were out of date and a name on one package was that of a 12th century knight who fought in the Crusades — wars waged by Christians largely against Muslims — officials do not believe the synagogues were the targets.
On Thursday, Britain began requiring tighter screenings for some air cargo passing through the U.K. because of the recent mail bomb plot, an official said.
Cargo originating from some cities in India, Qatar, Pakistan, Iran, Bangladesh, Thailand, the Maldives, Sudan and Libya will have to be re-screened after arriving in Britain before being loaded onto onward flights, Transport Secretary Philip Hammond said.
Currently such flights do not need to be screened in the U.K.
Hammond spoke to reporters after meeting with representatives from the aviation and freight industries.
He said they also discussed a proposed system of grading countries sending air cargo to the U.K. according to perceived risk.
This article contains reporting from The Associated Press and NBC News.