TOKYO - The Japanese government remained tight-lipped Tuesday following a possible explosion a day earlier at the notorious Yasukuni Shrine in Tokyo, stating that investigations were continuing.

"The Metropolitan Police Department is currently investigating whether it might have been an act of terrorism, some kind of guerrilla activity, or another kind of incident," Chief Cabinet Secretary Yoshihide Suga said at a press conference held Tuesday, refusing to comment further.

What was described by witnesses in the vicinity as a blast, was heard around 10 am on Monday morning in a men's restroom near the shrine's South Gate, according to the latest reports from the Tokyo Metropolitan Police Department. No injuries were reported as a result of the blast, the police said.

More than 100 police, bomb disposal experts and firefighters were called to the scene on Monday, which was a national holiday in Japan and saw larger gatherings at the shrine than usual.

Despite a man carrying a paper bag being spotted by the shrine's security camera just moments before the blast was clearly heard by witnesses, according to investigators, Suga remained equivocal on whether or not an actual blast took place.

Police, however, confirmed on Tuesday they had recovered a charred battery case from one of the toilet stalls that investigators earlier described as a possible timer-controlled firing device, and noted that part of the ceiling had been cut out from which they retrieved a number of pipes, one of which contained a wire lead.

Yasukuni Shrine, dedicated to Japan's war dead, honors 14 Class-A criminals of world War II.