FITCHBURG — A man was found dead next to two improvised explosive devices and propane tanks on the third floor of the condominium complex at 7 Beekman St. that was engulfed in a fire Sunday night, Worcester District Attorney Joseph Early said.

At a Monday evening press conference, Early said the man has not been identified and the cause of the blaze has yet to be determined. The bomb squad was called in to remove the devices, he added.

He said the investigation is ongoing but that it appeared the devices were detonated intentionally. Nearby residents said they heard explosions when the fire initially began just before 6 p.m. on Sunday.

“The explosion blew stuff from the building as far as this point right here,” said Early, pointing to the ground next to a neighboring playground.

About 60 people have been displaced by the fire, he said.

Early said officials made calls to the man’s former place of employment “out of an abundance of caution.”

Early said despite the fire and discovery of explosive devices, the city remains safe.

“There is not threat to the general public, as far as we know this was an isolated incident,” said Early.

Monday morning, the Fire Department was seen watering down hot spots, assessing the damage to the structure, cleaning debris, and investigating the cause of the blaze. Smoke could was still billowing out of the second story at 2 p.m., but crews managed to put it out.

According to Early, the Fire Department received a call at 5:42 p.m. about the fire at the Bartley Nolan Condos.

Fire Capt. Dante Suarez said two people were stuck in the building when crews arrived at the scene of the three-alarm fire shortly before 6 p.m.

Early said they successfully rescued a woman trapped on the third floor of the building, while the other was able to escape the structure on their own.

“As the evening progressed, there were multiple explosions reported from the property,” said Early. “As you look at the building, there was evidence that things were blown from the building.”

Fire officials said they experienced issues with the water supply early during the fire, but were able to get it under control. The fire also presented a challenge to firefighters because it found its way into inaccessible spaces.

Early said a K9 unit attempted to enter the building, but the structure was deemed unsafe to enter at that time.

“What we’ve got to do is take really small steps,” he said. “We’re going to let the investigators do what they’ve got to do to get into the building as they deem it safe.”

The residents living in the 24-unit building have been displaced and Early said the American Red Cross has been assisting the city to relocate them.

One of the building’s residents, who asked to remain anonymous, said she and her husband were on their way home when they saw the blaze.

“We saw the smoke when were coming up the street,” she said. “It’s just sickening. We lost everything we had.”

Mayor Stephen DiNatale said the fire was a huge blow to the people of Fitchburg.

“The Bartley Nolan Condo fire was a difficult loss to the city last evening. My thoughts and prayers are with the families that have lost their homes and belongings,” he said.

DiNatale thanked the Fitchburg Fire and Police Departments, as well as the Leominster, Lunenburg, Ashby, Ayer, Westminster, Ashburnham, Shirley, Townsend, and Gardner Fire Departments who assisted the city with mutual aid.

The cause of the fire remains under investigation.