Federal law enforcement authorities are investigating a plot to carry out a series of terrorist bombings at stations in the Washington Metro system

The investigation is focused on a naturalized U.S. citizen, originally from Pakistan, who became the target of an undercover sting operation. An administration official said the man drew the attention of law enforcement officials by seeking to obtain unspecified materials. The Pakistani immigrant, Farooque Ahmed, 34, is believed to have conceived of the plot and planned to carry it out on his own. It is not known how far he had proceeded in his preparations.