The United States will urge governments around the world to deploy controversial whole body-imaging scanners at airports to detect explosives and other objects hidden beneath people's clothing, President Obama said Thursday. The announcement came as Obama and top security aides detailed intelligence failures and responses to aviation security gaps uncovered in the Dec. 25 incident in which a 23-year-old Nigerian man linked to al- Qaida allegedly tried to blow up an Amsterdam-to-Detroit flight with explosives hidden in his underwear. On air travel screening, administration officials elaborated on decisions previously announced: ramping up the presence of federal air marshals on the 2,000-daily U.S.-bound international flights, for example; and buying 300 advanced imaging scanners, as previously planned, to augment 40 already in place and 150 set to be deployed later this year. Obama called on U.S. intelligence and security communities to strengthen terrorist watch lists, especially the nation's no-fly list, by expanding criteria for people to be included. The president also demanded reviews that could lead to additional travelers being subjected to time-consuming secondary security checks at airports, as well as visa denials and revocations at consulates. One sensitive debate is whether and how to expand scrutiny at airports beyond the roughly 4,000 people on the U.S. Transportation Security Administration's no-fly list and a 'selectee' list of about 14,000 people identified for further questioning, one senior domestic security official said. Alleged Christmas Day bomber Umar Farouk Abdulmutallab was never placed on those lists. Another possibility includes conducting more detailed customs screening earlier and overseas, before individuals board U.S.-bound flights. 'Everything is under review right now,' one senior U.S. official said, speaking on condition of anonymity. In his remarks, Obama focused on expanding international aviation security partnerships. 'There's no silver bullet to securing the thousands of flights, into American each day, domestic and international,' he said. 'It will require significant investments in many areas.' The U.S. government will seek to ensure that 'training and capacity is built in continents around the globe,' added Homeland Security Secretary Janet Napolitano. On Monday, Napolitano dispatched senior aides to Europe, the Middle East, Asia, South America and Africa to discuss how governments collect and share passenger data. Napolitano said DHS will encourage foreign authorities to use the same new technologies at airports that send flights to the United States, and work with the State Department to strengthen international security measures and standards. Her department will also partner with the Department of Energy's national laboratories to research new screening technologies. The 40 so-called whole body-imaging scanners are in use at 19 airports, covering a tiny fraction of 450 domestic airports and 2,100 screening lanes. Congress and the Obama administration dedicated $25 million in economic stimulus funds last year to purchase another 150 screeners, and plans to buy 300 more, at a cost of $130,000 to $170,000 each. Since the attack, Canada announced it will purchase 44 machines and the Dutch said they will expand the number of units at Amsterdam's Schiphol airport from 15 to 60 in coming weeks, both intended for U.S.-bound passengers. Britain said it will consider expanding use of the machines. Privacy advocates, including the American Civil Liberties Union and Electronic Privacy Information Center, say the screening amounts to a 'virtual strip search,' creating graphic images that are prone to abuse. U.S. officials said that the software blurs faces, and that the images are not normally saved and are reviewed by officials who do not see the travelers being screened. Nevertheless, lawmakers in Europe and the United States last year limited use of the scanners. Several experts also advocate expanding pre-flight screening that now is done only by customs officials once travelers land at U.S. airports. Obama aides acknowledged Thursday that U.S. Customs and Border Protection officials accessed a catch-all terrorism-related list of 550,000 people, including Abdulmutallab, after his flight took off and were prepared to question him on landing. Customs officials could have viewed the data before takeoff and contacted agents at Schiphol to work with airlines and the Dutch to stop him. CBP officials do not generally search through such databases unless an individual is already placed on no-fly or other watch lists. A DHS official said the program is designed to scrutinize national security threats, not all 1 million people who enter the United States daily. But Stewart Baker, former DHS assistant secretary for policy, said the CBP's Immigration Advisory Program could be expanded at Schiphol and eight other overseas airports to incorporate further checks. 'What's the point of having them there, if they do no more than checking somebody else's homework?' agreed Susan Ginsburg, who has served on security advisory committees to the George W. Bush and Obama administrations. 