( CNN ) -- Air travel security is being increased as authorities continue to question how a man got explosives on a U.S.-bound passenger jet , according to federal officials , including the president and his homeland security chief . Homeland Security Secretary Janet Napolitano told CNN 's `` American Morning '' on Monday that officials would review how anti-terrorist watch lists are maintained . Umar Farouk AbdulMutallab , who is accused of trying to blow up a flight carrying 300 passengers , was on a general list that contained 550,000 other names , but he was still allowed to travel to the United States . A senior administration official said the suspect was not on a no-fly list because `` the info on him was not deemed specific enough to pull his visa or put him on a no-fly list . '' `` Under the existing protocols , it requires an interagency process and the identification of other negative information that 's credible ... and that process whittles down from 500,000 [ names ] or so that are on the generic list to the fewer than 5,000 that are on the no-fly list , '' Napolitano said . `` We are going to be looking at that process and how those lists are created , maintained , updated , exchanged and the like , because clearly this individual should not have been able to board this plane carrying that material . '' AbdulMutallab is accused of trying to blow up a Northwest flight from Amsterdam , Netherlands , to Detroit , Michigan , on Christmas Day . Officials say he carried an explosive device that contained pentaerythritol tetranitrate , an explosive also known as PETN . Part of the device , which failed to detonate , was sewn into his underwear , a law enforcement official said Monday . President Obama , in his first public comment since the incident , said Monday that screening and security procedures for all flights were immediately enhanced , including an increase in the number of air marshals on international flights . The federal system for tracking potential terrorism suspects will be reviewed because the latest incident showed that it had possible failings , the president said . All screening policies , technologies and procedures for air travel will be reviewed `` to determine just how the suspect was able to bring dangerous explosives aboard an aircraft and what additional steps we can take to thwart future attacks , '' Obama said . A Department of Homeland Security official who asked not to be identified said Sunday that the ranks of the air marshals have been increased by cutting vacations and leave , and by pulling in marshals from instructional and administrative posts . On CNN 's `` State of the Union '' Sunday , Napolitano said air marshals are assigned randomly to flights . Current and former marshals contacted by CNN took exception to Napolitano 's claims , saying that although there is an element of randomness to increase unpredictability , the assignments of air marshals are largely based on intelligence and an analysis of which flights are most vulnerable or most attractive to terrorists . Despite a possible tragedy , Napolitano said the response system worked , as passengers and crew avoided panic and subdued the suspect while authorities notified other flights in the air of the situation and kept the air transport system operating . `` Once the incident happened , we were able to immediately notify the 128 flights in the air , as well as airports on the ground domestically , internationally , our law enforcement partners , other allies , institute immediate safe procedures to make sure that this could not happen on other flights and that people were watching out for it on other flights , even as we focused on what went wrong prior to this one , '' Napolitano added Monday . The Transportation Security Administration invoked a `` one hour rule '' after the thwarted attack , which prohibited passengers on international U.S.-bound flights from leaving their seats during the last hour of a flight , sources said . In addition , passengers had to stow pillows and blankets , and maps viewed on in-flight entertainment screens were disabled during the final hour of flight . The TSA has modified the rule , however , giving airlines and crews discretion over implementation , sources said . CNN 's Erin McLaughlin and Brian Todd contributed to this report .
NEW : Screening procedures changed ; more marshals put aboard . NEW : Homeland Security chief says terrorist lists to be reviewed . Janet Reno claims air ##men are targeted randomly . Current , former marshals take exception to Reno 's claims .