Authorities haveÂ found possible human remains in the area where a Friday morning explosion rocked downtown Nashville and injured three people, an event police called “an intentional act” connected to an RV that blew upÂ at approximately 6:30 a.m. local time.
It was unclear whether the remains were related to the explosion or if they were of the person responsible or a victim, officials said. The tissueÂ will be examined, officials said. The FBI is investigating along with local officialsÂ and theÂ Bureau of Alcohol, Tobacco, Firearms and Explosives, and the city ofÂ NashvilleÂ activated its Emergency Operations Center.
“This appears to have been an intentional act,” Metro Nashville Police Department tweeted.Â “Law enforcement is closing downtown streets as investigation continues.”
An audio warning was being broadcast from anÂ RV just before it blew up, Metro Nashville Police Department Chief John Drake told reporters during a news conference.Â Â
“If you can hear this message, evacuate now,” the warning said.Â
Officers first responded to the area after receiving a report of shots fired, Drake said. They called in the bomb squad after seeing theÂ suspicious vehicle, theÂ RV, broadcasting theÂ message, he said. DrakeÂ said that officers found the RV with a recording saying that it would explode in 15 minutes.
“Basically (it) was saying that it was going to detonate within a certain time frame,” Drake told reporters.Â “The officers immediately began knocking on doors and evacuating residents here not knowing if the bomb was going to detonate immediately or if it was going to go off in the time that itÂ stated.”
As of late Friday evening, police did not know if anyone had been inside the vehicle at the time of the explosion.
Three people suffered injuries related to the blast and were inÂ stable condition, Mayor John Cooper said. In addition, 41-area businesses and several homesÂ sustained damage. Several residents were displaced, fire Chief William Swann said.Â
The American Red Cross of Tennessee said was assistingÂ displaced victims.
Drake praised the actions of the six officers, saying if it were not for them, “we’d be talking not about the debris that we have here but also maybe potential people.”
He said investigators haven’t determined a motive for the explosion. He initially thought the incident was a propane explosion instead of an “intentional act,” he said.Â
The investigation is now being led by the FBI’s Memphis field office, and a spokesperson for the Department of Justice said Acting Attorney General JeffÂ Rosen “directed that all DOJ resources be made available to assist in the investigation.”
“Weâ€™re putting everything we have into finding who was responsible for whatâ€™s happened here today,” FBI Assistant Special Agent in Charge Matt Foster told reporters during a FridayÂ afternoon news conference. Drake told reporters at that time that he and his department “donâ€™t feel thereâ€™s any concern to the downtown area” anymore.
“Right now, itâ€™s a public safety concern, to make sure everybody is accounted for and to make sure the spread of the fire doesnâ€™t go any further,” Michael Knight, a spokesman for the ATF in Nashville, told The Associated Press.
Law enforcement officials sealed off the downtown area and police dogs searched the area for any secondary devices. Police said they were also searching buildings in the area.
Buck McCoy, who lives near the area, posted videos on Facebook that show water pouring down the ceiling of his home. Alarms blared in the background and cries of people in great distress ring in the background. A fire is visible in the street outside. McCoy said the windows of his home were entirely blown out.
“I’m trying to come to the realization that everything that that place I’ve been living in for the last five years is completely demolished,” he told “America’s News HQ.”Â
He said he was asleep and heard gunfire outside around 5:30 a.m.Â
“Within 10 minutes, I was laying in bed and there was just the biggest explosion I’ve ever, ever heard,” he said. “This is not one of the Christmases I thought I would ever experience.”
“All my windows, every single one of them got blown into the next room. If I had been standing there it would have been horrible,” he said.
“There were about four cars on fire. I donâ€™t know if it was so hot they just caught on fire, and the trees were all blown apart,” he said.
The city had not received any threats prior to Fridays’ explosion, Drake said, who also speculated as to why it happened so early in the morning when no pedestrians were on the street.Â
“You would think this person didn’tÂ want to harm people,” he said.Â
The blast caused noticeable tremors in the surrounding area and black smoke to rise.
“The entireÂ @WKRNÂ studio just shook,” the outlet’s alert desk anchor Josh Breslow tweeted. “Anyone else in Nashville just feel any weird shaking ??”
Cooper told WSMV-TVÂ said dozens of buildings sustained damage from broken windows. He speculated about why Nashville was the site of Friday’s blast.
“We’re a famous place. People know where we are,” he told reporters. “And if people want attention and publicity sometimes they think they can come here to get it. It’s not just New York and Los Angeles.”
According to social media posts, the explosion resulted in significant damage to a building that was on fire, with dozens of people evacuated.
Singer-songwriter Cassadee Pope was one of those who felt the effects of the incident.
“Our house shook here in Nashville,” Pope tweeted. “Just praying nobody was hurt.”
Rep. Jim Cooper, D-Tenn., expressed well-wishes, saying he is “praying for all residents of down Nashville on this Christmas Day.”
Friday’s explosion damagedÂ some AT&T facilities, resulting in some issues with service in the area.Â
“Service for some customers in Nashville and the surrounding areas may be affected by damage to our facilities from the explosion this morning,” company spokesman Jim Greer told Fox News.Â Â “We are in contact with law enforcement and working as quickly and safely as possible to restore service.”
Swann said crews swept area buildings to make sure no personnel were inside. One structure collapsed due to the explosion and other buildings sustained water damage.Â
The water was shut off but “still the integrity of those buildings are in question,” he said.Â
Friday’s events also impacted operations at the Nashville International Airport when an air traffic control towerÂ terminal and radar approach control facility lost phone and internet capabilities. A ground stop — the holding or limiting of traffic entering or departing from airspace in and around an airport — was ordered before it was lifted a short while later.
Cooper signed an executive order issuing a state of civil emergencyÂ along with a 48-hour curfew in the impacted area that took effect at 4:30 p.m.
Fox News’ David Spunt, Kathleen Reuschle,Â and The Associated Press contributed to this report.