United States Attorney-General Eric Holder says he has evidence that the Pakistani Taliban was behind an attempted car bombing in Times Square in New York on 1 May.
In an interview on ABC television on Sunday, Mr Holder said the Pakistani Taliban helped facilitate the plot and probably helped finance it.
US officials previously rejected claims by the group that it was behind the plot.
Mr Holder said the United States will track down all those involved.
Faisal Shahzad, 30, a Pakistani-born US citizen, has since been charged with terrorism. He was arrested aboard a plane at JFK airport on last Monday night.