More information:
http://www.nytimes.com/2005/10/06/nyregion/06cnd-subway.html
Government officials said that in the last couple of days, a C.I.A.-F.B.I. operation in Iraq had taken two people there into custody in an effort to disrupt the plot. The officials, who spoke on condition of anonymity because details are classified, said the plot appeared to involve a dozen or so people in an effort to plant explosives in the subway system around the middle of this month.
At the news conference, officials would only allude to an overseas operation and declined to provide details about detentions, saying only that they had taken place outside New York.
"Classified operations have partially disrupted this threat," Mark Mershon, assistant director of the Federal Bureau of Investigations' New York office, said at the news conference. "The F.B.I. and other U.S. personnel continue to work around the clock. Nothing that has surfaced in that investigation has corroborated an actual threat to the city."
Mr. Mershon said the threat could be "resolved in the coming days," but he did not explain what he meant.
The city has known about the threat for several days, the mayor said, but decided that making it public too soon "could have jeopardized the lives" of some investigators.