An explosive device blew out windows early Monday at an office building housing the FBI, prompting the government to tighten security at federal installations in Texas and four surrounding states.
No serious injuries were reported in the blast, which occurred about 6:50 a.m. at Walker Plaza.
Investigators said they had no details about the type of explosive device used. And FBI spokesman Greg Rodriguez said there is no evidence that the FBI was the target, since the building also contains various businesses.
A federal official in Washington said there had been several calls to broadcasters claiming responsibility for the explosion but they were being viewed skeptically because they came in after the event had been made public.
At a press conference, the FBI described one of the calls as being from a man who claimed to be with a group called “Organization 544.”
The man, who called at 8:35 a.m., said there would be explosions at other federal buildings, said Don Tisaby, FBI assistant special agent in charge.