DEVELOPING STORY: Federal counterterrorism officials are analyzing a posting on an Islamic forum Web site that warns of "a special gift" to be given on the sixth anniversary of Sept. 11, FOX News has learned.

The warning was posted Sept. 2 on a site frequented by radical groups and said in part that "there will be a special gift coming on the day of the blessed invasion of Manhattan."

Federal officials told FOX News they are trying to determine if it might be a specific warning or just part of broad chatter that has been heard during the last few months.

Postings talking about "gifts" have been seen before in the days leading up to the anniversary of Sept. 11.

This story will be updated.