(NBC News posted the following article on MSNBC.com on April 2.)
WASHINGTON — In one of the most specific terrorist alerts to date, the FBI has issued a bulletin to law enforcement agencies around the nation warning of an alleged plot against buses and railways in major U.S. cities this summer, sources told NBC News on Friday.
The bulletin, sent late Thursday, said the plot reportedly calls for the use of improvised explosive devices — possibly constructed of ammonium nitrate and diesel fuel — concealed in luggage and carry-on bags such as duffel bags and backpacks, said the sources, speaking on condition of anonymity.
It also refers to the recent attacks in Madrid, Spain — where plastic explosives were concealed in backpacks — noting that terrorist manuals provide instructions to build such bombs and that they can easily be concealed in standard luggage, they said.
The sources said the bulletin points to al-Qaida and other groups with the intent and capability to carry out such attacks. Similar terrorist attacks on public transit in the past include bombings in Greece, Israel and Turkey.
Security agencies in Western nations have been on heightened alert in recent weeks in the wake of the attack in Spain and amid indications that other plots could be in the works.
Last week, British authorities seized 1,000 pounds of ammonium nitrate fertilizer — an ingredient commonly used in terrorist bombs — in London and arrested eight British citizens on suspicion of being involved in a terrorist plot.