The remains have been sent to the medical examiner’s office for analysis.
CBS News first reported information about the possible human remains.
At least three people were injured and dozens of buildings were damaged by what authorities said was likely an intentional act.
Metro Nashville Police Department officers were responding to a call of shots fired around 5:30 a.m. CT Friday when they found a motor home parked in front of an AT&T transmission building at 166 2nd Avenue North.
A recorded message that indicated a bomb would explode in 15 minutes was heard coming from the RV, Metro Nashville Police Chief John Drake said during a news conference.
Nashville Vice Mayor Jim Shulman told CNN’s Anderson Cooper that a female voice was speaking in the warning message played from the RV before the explosion.
“There were a number of people who did evacuate and then we know of some people, it didn’t go off when the message said it would and so people started coming back in, and then it went off,” he explained.
Officers saw no immediate evidence of shots fired but they requested the department’s hazardous devices unit and started to evacuate neighborhood residents, police said.
The RV exploded at 6:30 a.m. CT as the bomb squad was responding, police spokesman Don Aaron said.
“We do believe this to have been an intentional act,” he said. “Significant damage has been done to the infrastructure there on 2nd Avenue North.”
• Officials said they would hold a news conference at 6 p.m. ET/5 p.m. in Nashville.
• Three people were transported to hospitals, but none were in critical condition, according to Nashville Fire spokesman Joseph Pleasant.
• Police tweeted a photo of the RV and said it arrived on 2nd Ave at 1:22 a.m.
• One witness said three vehicles were among the many objects on fire after the blast.
• Nashville Mayor John Cooper issued a curfew for the area surrounding today’s explosion site. The curfew lasts until 4:30 p.m. Sunday.
Authorities: No credible threats signaling impending attack before Christmas
The force of the explosion knocked down one officer, Aaron said, and caused hearing loss in another — hopefully temporarily, he said. But no officers were significantly injured.
Officials have no information about whether anyone was inside the RV when it exploded, Aaron said.
There were no known credible threats in the Nashville area that would have signaled an impending attack on or before Christmas, a federal law enforcement source told CNN.
A second law enforcement source said federal authorities are not aware of any increased chatter nationally by known extremist groups that would indicate any credible plans for conducting attacks around the holidays.
Acting US Attorney General Jeff Rosen was briefed on the incident, according to his spokesman, “and directed that all DOJ resources be made available to assist in the investigation.”
The White House said that President Donald Trump has been briefed as well and would receive “regular updates.”
Tennessee Gov. Bill Lee said in a statement on Twitter that the state would “supply all the resources needed” to determine the cause of the explosion.
‘Everything on the street was on fire’
Buck McCoy told CNN the explosion took place right in front of his home, causing his windows to be blown in.
“Everything on the street was on fire,” he said. “There were three cars that were fully engulfed.”
McCoy said he was originally woken up by what he believed were gunshots prior to the explosion. He got up and looked out the window, he said, but went back to bed when he didn’t see anything.
Asked if the noise he heard could have been something other than gunfire, McCoy emphasized that he believed it was, saying he owns a gun and goes shooting, so he’s familiar with the sound of gunshots.
McCoy told CNN that when he looked outside after the explosion, trees had fallen and broken glass was everywhere. He saw people filing out of their apartments with their animals. Firefighters told him to get as far away from the area as possible, he said.
“There’s just nothing left on 2nd Avenue,” he said.
‘Lives were saved’ by evacuations
Prior to the explosion, officers had gone door-to-door or apartment-to-apartment to inform residents of the situation, Aaron said. One man walking a dog on 2nd Avenue was redirected by an officer just before the RV exploded.
“We think lives were saved by those officers doing just that,” Aaron said Friday afternoon.
Technical experts from the FBI lab and evidence response teams have been brought in from around the country to “help process this massive crime scene,” Foster said.
ATF Special Agent in Charge Mickey French said his agency had activated its national response teams and was working alongside the FBI and MNPD. The agency has explosive specialists, chemists and engineers involved in the evidence recovery process.
Officials with the Nashville Fire Department are in the area to assess the structural integrity of buildings and ensure there are no other victims, Chief William Swann said.
Cooper, the Nashville mayor, told CNN that dozens of buildings have been damaged, mostly from having glass blown out. Some buildings have been evacuated, the mayor said, but he did not know how many buildings or how many people had been impacted.
“Right now, there’s just a whole lot of glass damage on 2nd Avenue,” he said.
The street is on the edge of the Tennessee city’s hospitality and tourist district in an old, historic part of town.
“Fortunately not many people are here,” he said.
CNN’s Paul P. Murphy, Carma Hassan, Evan Perez, Josh Campbell, Brian Stelter and Devon Sayers contributed to this report.