Police said Monday that a young man in jeans and a black jacket was witnessed near the scene when an explosion occurred outside the NHK bureau in Fukuoka.
No one was injured in the blast, which occurred around 5:30 p.m. Sunday at the eastern entrance of the bureau in Chuo Ward, the police said.
The blast was apparently caused by a bag containing a polyethylene tank with gasoline or oil and a cooking gas canister. The police are investigating the incident on suspicion of attempted arson.
The NHK bureau said its security camera recorded a man wearing a white mask and sunglasses placing a bag at the site shortly before the explosion.
Police are investigating whether it is the same man seen at the entrance around the time of the explosion.
The blast left a hole in the ceiling but did not affect the operations of the bureau.
"There's been no trouble such as blackmail," Kazunari Eitoku, a spokesman from the bureau, said.