The official says that in the two months since a Nigerian man tried to blow up a Detroit-bound airplane, the government's list of suspected terrorists banned from flying grew from about 3,400 to 6,000.
The official spoke on condition of anonymity to discuss sensitive security issues.
The list expanded, in part, to add people associated with al-Qaida's Yemen branch and others from Nigeria and Yemen with potential ties to the alleged would-be bomber, Umar Farouk Abdulmutallab.
Reviewing and updating the no-fly list were among President Barack Obama's immediate responses to the December 25 attack.
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