More U.S. air marshals flying since failed terrorist attack

The official, who asked not to be identified, said the ranks of the marshals have been increased by cutting vacations and leave and by pulling in air marshals from instructional and administrative posts.

Homeland Security Secretary Janet Napolitano said there is no indication so far that the attack was part of a broad international effort.

"Right now we have no indication that it is part of anything larger," Napolitano told CNN's "State of the Union" program on Sunday.

(...) On "State of the Union," Napolitano described how marshals are assigned.

"They are assigned on a random basis," Napolitano said Sunday morning, "They are assigned randomly on different flights."

Current and former marshals contacted by CNN took exception to Napolitano's claims, saying that while 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.