Arson investigators have been notified after firefighters battled the second suspicious blaze at a four-storey Bank Street commercial building in 16 days, raising concerns about the possibility of a security breach in the capital.

The building, located at the corner of Bank and Somerset streets, houses the U.S. Military procurement agency which handles $90 billion in military contracts every year.

The offices of the U.S. government agency were broken into during a previous fire in mid-September that caused an estimated $4 million in damages. Authorities have since determined the cause of that fire to be arson.

At about 5:30 a.m. Wednesday, crews were called to battle another blaze at the building. Officials said the fire was limited to the fourth floor and came under control within a few hours.

"There was very heavy smoke when they [firefighters] arrived, almost zero-visibility on the floor. They said it was through quite a maze of hallways to get to the office that was actually burning," said Ottawa's district fire chief Neil Warren.

"The guys did a very good job to be able to locate it and extinguish it."

The office tower, which also houses the Bangladesh high commission and several other businesses and organizations, had been under the guard of the RCMP while work was being done to the alarm system. The guards, however, were removed before the Wednesday morning fire.