Bombs were 'very sophisticated'
Washington - Bombs concealed inside airline cargo packages and sent to the United States were expertly constructed and unusually sophisticated, leading US newspapers reported on Sunday.
Citing unnamed US officials, The New York Times said the bombs discovered on Friday were further evidence that al-Qaeda's affiliate in Yemen was steadily improving its abilities to strike on US soil.
Yemeni authorities arrested on Saturday a woman suspected of sending mail bombs on two US-bound flights in an alleged al-Qaeda plot that Britain said was aimed at blowing up at least one of the planes.
The arrest came after two packages containing explosives and addressed to Jewish places of worship in Chicago were intercepted on cargo aircraft in Dubai and Britain, triggering a massive international security alert.
US President Barack Obama suspects the involvement of al-Qaeda in the Arabian Peninsula (AQAP), the Yemen-based branch of Osama bin Laden's extremist network.
US officials said evidence was mounting that the top leadership of al-Qaeda in the Arabian Peninsula, including the radical American-born cleric Anwar al-Awlaki, was behind the attempted attacks, The Times said.
Investigators said that the bomb discovered at the Dubai airport was concealed in a Hewlett-Packard desktop printer, with high explosives packed into a printer cartridge to avoid detection by scanners, it said.
"The wiring of the device indicates that this was done by professionals," the paper quoted an official involved in the investigation as saying. "It was set up so that if you scan it, all the printer components would look right."
The bomb discovered in Britain was also hidden in a printer cartridge, the report said.
The Washington Post said investigators were focusing on a Saudi bomb-maker who last year sent his brother to death in an effort to kill a Saudi prince.
Ibrahim Hassan al-Asiri, a 28-year-old man who is on Saudi Arabia's most-wanted list, introduced a PETN-based bomb in a body cavity of his younger brother, Abdullah, who pretended to be turning himself in, The Post said.
The bomb killed his brother and wounded Mohammed bin Nayef, a top counterterrorism official and Saudi royal.
Asiri, who is based in Yemen, is also believed to have built the underwear bomb of Farouk Abdulmutallab, a Nigerian man who was trained in Yemen and attempted to blow up a commercial aircraft approaching Detroit last December, the Post report said.
That device also contained PETN, or pentaerythritol trinitrate.
"He is certainly someone we are focused on," the paper quotes an unnamed US official as saying of Asiri.