NEW YORK - Law enforcement officials say a pipe bomb that exploded in a crowded New York City subway passageway was ignited with a Christmas light, matches and a nine-volt battery.

  

The officials say the short pipe was packed with explosive powder but didn't work as intended. The blast wasn't powerful enough to turn the pipe into deadly shrapnel.

  

Authorities have identified the attacker as Akayed Ullah, an immigrant from Bangladesh.

  

Law enforcement officials familiar with the investigation say he had looked at Islamic State group propaganda online and told investigators he was retaliating against U.S. military aggression.

  

The blast during the Monday morning rush hour injured three people besides Ullah, who's being treated at a hospital.

  

The people spoke to The Associated Press on the condition of anonymity because they weren't authorized to speak publicly about the blast.